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Evidence of Re-Innervation in EMG findings

In terms of reinnervation findings of EMG, including increased recruitment, instability of MUP, increased Amplitude of MUP (?), etc, which of these features are reliable to predict the true re-innervation in morphology? The reasoning process of EMG physiology is not specific to predict morphological changes.

Answer 1

One of the first things to appear after denervation is fibrillations and positive waves of course. Following that (in about 2 months) the first signs of reinnervation are an increase in the number of phases of a motor unit, polyphasic potentials (check out: https://www.teleemg.com/new/jbr120.htm Neurogenic Motor Unit), and increased instability of the MUAP (high jiggle) with decreased recruitment followed by an increase in the amplitude.

Answer 2

Further comment on evidence of reinnervation in addition to concentric EMG findings. The Fiber Density (FD) increases after reinnervation due to collateral sprouting. The increase of FD indicates that muscle fibers increased for the same motor unit. The FD therefore, is a most sensitive method to quantify reinnervation, and therefore, the local organization of motor unit (morphology!). Also, FD corresponds to type grouping in pathology.

EMG Technique (fasciculations)

Is there a way to distinguish between benign and malignant fasciculations ELECTROMYOGRAPHICALLY and most of all CLINICALLY? Is it true that rhythmic fasciculations tend to be benign while a singular big thumps tends to be malignant? is it true that brief fasciculations tend to be benign. Is it true that coarse fasciculation are usually benign while the malignant ones are very fine ones? What of all that is true and how it reflects in EMG.

Answer 1

This is a very common concern and generally no single answer is satisfactory because almost every single rule you make to define a benign versus malignant fasciculation has an exception. Generally speaking though I can tell you that Neurologists rely on far more than the presence (or absence) of fasciculation potentials to make the diagnosis of ALS. If fasciculations become worrisome to a patient, I generally recommend they seek a qualified neurologist’s opinion to ease their fears, because the worst thing they can do is to self diagnose them with the disease.

Answer 2

The best measure of benign versus malignant fasciculation potentials comes from the EMG needle exam by the company they keep…in other words… if fibrillation potentials and positive sharp waves are present with large motor unit potentials and polyphasic waveforms with poor recruitment…along with fasciculations…this would tend to suggest a more ominous potential…A good history and physical exam is a priority…remember an EMG exam is only an extension of our physical examination.

Single Fiber Amplifier Settings

I am having a minor debate on Amplifier settings for SFEMG. (I believe the Filters were changed on my system.) What are the recommended settings and have there been any recent changes in them? Specifically, I am concerned about the Low Frequency Filter Setting. What would be the upper limit? What is the typical setting?

Answer

The recommended or typical filter settings are LFF 500 Hz and HFF 10 KHz. I may use LFF 1KHz (narrower settings). This LFF setting would reduce the disturbing distant muscle fibers. This setting, however, affects the shape of the single fiber potential. But it should not affect the jitter value or fiber density reading. I am not aware of recent changes. However, if detailed measurement is needed for the shape of action potential, then use more open filter settings LFF 2 Hz and HFF 20 KHz.

Theoretical guidelines vs. practical for thoroughness of EMG studies

Having read the guidelines in the online EMG manual for the thoroughness of the study of a muscle (i.e. testing 20-25 units for both spontaneous and voluntary activity, calculating average amplitude phase etc.) I am curious why it seems these guidelines aren’t followed more often. Having had a number of EMGs in the past year in both local and university settings and in all cases only 3-4 units (1 insertion 3-4 directions) was sampled. One of these EMGs was overseen by a very renowned name in Electromyography (no names, but odds are you have one of his books on your shelf,) and even then 1 needle insertion per muscle. In a dialog with a doctor who does follow these guidelines, I was told many of the patients he performs EMG on tell him that his study is far more thorough than that done by their own neurologist. I fully understand the reasoning behind the 20-25 MUP guideline if for no other reason than to increase diagnostic accuracy. My questions then are twofold. Do most Electromyographers routinely follow these guidelines or are they followed only when the situation/case dictates. Secondly, how much diagnostic accuracy is there when only 3-4 units per muscle are tested, for example during a MND workup, and no abnormalities are found?

Answer

I agree not all EMGers follow these guidelines, although I do catch myself sampling less frequently in follow-up studies when I am only looking for changes.

Comment

My EMGs have been done locally. I certainly understand your comment about less stringent testing when verifying a change. My main concern is with initial testing where the results are negative, no sign of any disease process. With what degree of certainty can the electromyographer state that the muscle tested is normal when only testing 3-4 units in that muscle? Are they any statistics or figures on how the number of units sampled in a muscle corresponds to diagnostic accuracy rates? I can calculate numbers based on basic probability theory but was curious if any formal studies or accepted statistics existed. Thanks again and kind regards.

Answer

Tough question to answer. I don’t know of any studies of predictive statistics (for the number of muscles tested vs. diagnostic accuracy rate) That would be an interesting study. As for number of units tested, naturally if you find the abnormality in the muscle early on (with 3-4 units), you don’t need to go any further. But if you don’t, the general rule of thumb is to be more thorough to increase your chances.

Answer 2

I agree it would be an interesting study. From a strictly mathematical perspective it should be fairly easy to compute the “odds” of finding abnormalities. This is a lot like the classic probability problem of given that a person throwing darts can hit the bulls eye x% of the time, how many times must they throw the dart to have a given percent chance of getting a bulls eye. In the case of EMG the “x” can be the percentage of units in the muscle involved in the disease process. The number of throws would be the number of units tested and percent chance of getting a bulls eye would correspond to the odds of hitting an involved unit. The equation for this would be: ln(a) = ( ln(i)) / (n)) In this equation the variables are: a – the percent chance of hitting an involved unit expressed as a decimal (i.e. 56% = .56) i – the percentage of units in the muscle involved in the disease process as a decimal n – the number of units sampled in the muscle I have made several assumptions in this equation. 1. The involved units are randomly distributed throughout the muscle. 2. When the needle hits an involved fiber, the pathological signs such as fibs, positive waves, polyphasic units etc. will be visible to the EMGer. 3. The insertion points will be randomly distributed across the muscle. This is not entirely accurate since there would probably only be 4-5 actual insertions through the skin and then testing in multiple directions to get the 20 units. However assuming the insertions were not all done in the same spot, the equation holds. The results of this calculation clearly show why sampling more units can yield more accurate results. Examples: Sampling 20 units in a muscle with 10% involvement gives you a 90% chance of finding an involved unit Sampling 4 units in a muscle with 10% involvement gives you a 56% chance of finding an involved unit. Sampling 20 units in a muscle with 25% involvement gives you a 93% chance of finding an involved unit. Sampling 4 units in a muscle with 25% involvement gives you a 70% chance of finding an involved unit. Sampling 20 units in a muscle with 50% involvement gives you a 97% chance of finding an involved unit. Sampling 4 units in a muscle with 50% involvement gives you an 84% chance of finding an involved unit. So sampling more units in a muscle greatly increases the chances of finding an involved unit, especially early in the disease process. Kind regards

Answer 3

I read the interesting discussion on this point. I believe that few additional factors may influence the number of motor unit tested. Firstly, the experience of the neurologist or electromyographer. Secondly, the clinical examination of the patient. And finally, the degree of patient’s cooperation during sampling. It is also, basically, the same argument could be applied to the number of F-waves should be obtained for shortest latency. My kind regards,

Answer 4

Very interesting subject. About 4 years ago I was in Italy / Milano/. At the very famous S.R. Hospital I saw the following practice. The electromyographer there does not catch even one potential at single muscle. They say to the patient to do a slight effort, then observe moving potentials (do not record), after e period of few minutes they made conclusions e.g. MUP with growth of amplitude and area. I asked them how long of a period is needed to become proficient in this method: – 3 months

Single proximal conduction block, significance?

How significant should a single or isolated motor nerve proximal conduction block be as diagnostic sign, for instance in multifocal motor neuropathy, inflammatory demyelinating polyneuropathy or the “new entity” the multifocal inflammatory demyelinating neuropathy. Occasionally, I come across such an isolated finding, rechecked to exclude technical.

Answer

No single “isolated” abnormality should be diagnostic for a specific lesion. What is the waveform morphology? Abnormal temporal dispersion is usually absent in MMN. “Inching” along the course of the nerve often can demonstrate if the CMAP diminishes abruptly as in MMN, or progressively as in chronic axonal loss or demyelination. What clinical signs are present upon examination? Asymmetric distal weakness generally is present in MMN versus symmetric, proximal weakness in CIDP. The presence of a single proximal conduction block across common sites of entrapment is not helpful in establishing a diagnosis of MMN.

NCV “latency”

The Latency that is measured: 1.Does it depend on the distance taken by the examiner? 2.Does it depend on the amount of electric stimulation (such as the CMAP amplitude)? 3.Is it better when high or low?

Answer

Yes, the latency depends on the distance, the greater the distance, the longer the impulse has to travel and the greater the latency. It also depends on the amount of electricity you use; if you are submaximal, you are not stimulating all the fibers and your measurement will be inaccurate. That’s why in nerve conduction it is advised that you use supramaximal stimulation which is maximal stimulation + 25% over that to ensure stimulation of all the nerve fibers.

Timing of benign vs. pathological fasciculations

One small question, in your electronic EMG manual you state that benign fasciculations generally occur at 8-second intervals whereas pathological ones occur at a slower rate of 3.5 seconds. In another online resource that has video files of EMG findings: http://www.med.ohio-state.edu/physmed/videos/EMGvideos.html They say the opposite, “Non-pathologic fasciculations usually recur at a very slow rate (less than 3 per 10 seconds), while pathologic fasciculations most commonly occur more frequently than 3/10sec.” While I know that without other EMG findings (or lack of) it is tough to say one way or the other if fasciculations are good or bad but I am curious about these different viewpoints. Thanks again for providing such a valuable resource!

Answer

I am aware of the discrepancy in the literature on benign vs. malignant fasciculations. Over the years, I find myself no longer regarding this as black and white but rather find myself relying more heavily on many factors such as the shape of the fasciculation potential their distribution and what else I am finding. For instance, the more complex and “polyphasic” the morphology, the more likely I am to consider them pathological (I don’t like the term “malignant”). Other factors that enter my mind is their widespread distribution and the presence of other signs of ALS such as fibs and positive waves and neurogenic units. So I now rely on the “environment” in which I find the fasciculations rather than on one or two factors alone. Thanks for your kind words.

Comment

Thanks for the reply. I understand your point about what else you find being the true diagnostic criteria. I am curious though which theory is “supposed” to be correct or is there no real consensus? Also if it isn’t too complex what is the reasoning behind one being “slow” and one being “faster?” Again thanks for taking the time to help not only me but all the people who come here with questions. With kind regards,

Computer assisted EMG!

I know that some of the neurologists use computer program for the analysis of EMG needle insertion results. However, I am not sure how advanced these computer programs are! In my EMG exam I got the results within minutes after it ended (normal) and the neurologist told me that his computer program makes much of the analysis for him rapidly – for example MOTOR UNIT ANALYSIS! He said this advanced program analyzes the motor units! MY QUESTIONS ARE: 1.Does it sound possible (motor unit analysis done by a computer program? 2. some of the results of a muscle were (motor unit) (tibialis anterior) AMP (normal), Duration (normal), poly (normal) STABILITY (normal) INTERFERENCE PATTERN (normal) Is there any computer program that can analyze these features of MUP “alone” – I mean check these MUPS features for the neurologist without he analyzing it by himself? MY question refers mainly to motor unit stability (but also AMP, duration, IP and poly) – can the computer check if the MUAPs are STABLE without the neuro “doing this job”, can the computer tell by “itself” the motor units are stable and not polyphasic?

Answer 1

It is amazing what computers can do. I think we have not seen anything yet, still more to happen in the future. I can recall an American association of EMG and Electrodiagnosis session in 1984 about role of computers in EMG by Joe Jabre and David Hampton. The Computer program was able from that time to perform MUP parameter analysis. The software is getting better. The point that the computer is willing to help but I think working experienced human brain is always needed to rectify the technical problems, for instance, quite frequently you need to correct the position of markers during MUP analysis otherwise you may end up having false prolonged polyphasic unstable MUP.

Answer 2

Thanks for this interesting question! The truth is computers have come a long way since the early 80’s and can “assist” EMGers a great deal but not make diagnosis. There are still a lot of things that an experienced EMGer can pick up that can be missed by the computer. More importantly if the recording electrode is not placed in the appropriate area of the muscle, you feed poor quality data to the computer and as the saying goes “garbage in, garbage out”. So yes computers can be very helpful but no they are not smart enough to replace humans.yet.

Comment

I know computerized EMG is of great value! Your insight on this fascinating use of computers will be highly appreciated! My question is: (using the most sophisticated computer programs) – does the computer calculates and prints out specific answers or just “normal”/”abnormal” – for example MUAP A. Stability – does its output is: “normal stability”/ “reduced stability”,/”slightly reduced” or just “abnormal stability”. And for B. amplitude and duration – can the computer calculate them and “decide” by its own – whether these are within normal ranges? C. And what about the IP – can it “distinguish” several levels of reduced IP or it can just decide “normal/abnormal”? * I would appreciate your insight on these 3 features of the computer analysis (stability,amp-dur and IP) * when It does this MUPS analysis by “ITS OWN” how many motor units does it check (10,20,30,40) How much time does it take for it to check this number of MUAPs (seconds???) THANK YOU FOR READING THIS AND I WOULD APPRECIATE YOUR INSIGHT!

Answer 1

Yes the computer does all those functions, but of course with manual help i.e. operator should accept/reject the potentials. The system can take any number of MUPs, the operator should again decide that number.

Answer 2

This is a very general question as you can gather and different machines have different programs for different tests so it is impossible to answer this in a “wholesale” fashion. However, as far as motor unit analysis is concerned, most programs used usually give printouts of measures (numbers) for amplitude, duration and number of phases and some do firing rate analysis. Some do Turns and Amplitudes analysis. Some of these numbers are generated as numbers and some are plotted against a “cloud” of normal reference values and those, which fall outside the cloud, are called abnormal. Generally speaking, and realistically, only 5-6 different motor units can be properly analyzed from one needle location, because, as more motor units are recruited, the tracing becomes too complex for the program to analyze and the data generated less reliable. Most programs today on commercially available equipment can reasonably follow a contraction up to 30% of maximum and after that they become unreliable. To do a reasonable computerized motor unit analysis, it usually takes anywhere between 30-45″ or up to a minute per insertion.

Comment

It was pleasure for me to have your insight on the computer assisted EMG issue. You said you do not know what program did he use: well, He said this “is the most sophisticated EMG program and that it is able to do mups analysis almost alone! Yet; another question. What about positive waves and fibrillations- Is the program capable of detecting (distinguish them from other activity) and count them and at last print How many of them there were? (I think HE said it can) The output of the computer was: (all the insertions) fibs -0/10 PSW- 0/10 What DO these numbers mean? Is there any computer, which can pick up fibs/PSW by its own, distinguish them, count them and print their number without the examiner doing that?

Answer

Sorry, I cannot comment on all the specifics as these vary greatly from system to system and EMGer to EMGer

Comment

My question is again about the use of computers in a regular EMG test. Is there any computer program nowadays that can pick up fibrillations, count them and distinguish each one of them by its own. And then output for example: “3 fibrillations”? I know that each fibrillation has its own rhythm so that is why I am asking if there is ANY computer program that is able of distinguishing each one of them and of course, recognizing a fibrillation and distinguishing it from any other activity and all by its own?????? (MY main question is about the ability of any computer program to identify and recognize a fibrillation and distinguish it from any activity)

Answer 1

In the ones I am familiar with it is the doctor that picks the number of fibrillations he or she sees in the muscle and enters them into a report generation software in the computer which then prints it

Answer 2

Although there is none at present time but it sounds like a potentially possible idea to make a computer program to do such fibrillation and PSW detection and counting, similar to spike detection in EEG. Perhaps, it is a matter of time

EMG “Interference & recruitment”

What about the interference pattern and motor units recruitment?? Is There any computer programs that can “decide”” if the IP was full? What is the output normal/abnormal or it can also distinguish different levels of poor recruitment?? and motor unit stability? What is the output in this case? (stable/unstable or various degrees)? * In my EMG the neurologist told me the computer does mups analysis all by its self within less than a minute per insertion The results were: “stability: normal, IP: normal” and he told me his new computer program can decide and check these two parameters by its own. Is it possible (regarding these two parameters)? And what would be the output (the question above)

Answer

Again not knowing the specifics I can only answer this question in general terms: The IP is (usually) studied with a program called the Turns and Amplitudes analysis. This is pretty rapid and can give an idea of the interference pattern. It usually plots the data inside a normal population cloud. If your data is inside the cloud the IP is OK, if it’s outside it is not. So the output here is graphic. Stability is decided upon by what is called a “jitter” between the various components of the motor units, and again, since motor units are only adequately analyzed at a 30% level of maximum, only those which could be appropriately analyzed can be called stable or unstable. So the output here essentially is text

60 Hz Electric interference

When putting the needle (in my EMG) in left triceps, there was a very steady wavy line instead of the normal straight normal line my neurologist just could not reach the desirable wavy line. (I think there was not any sound) – during voluntary activity everything was normal. IT was a steady (“sine like” or “snake like” wave) – I think It was not fibs- because there was no sound and fibs look more like spikes – mine were very very wide “tall”, “fat” regular steady waves. They were upward negative (thus, not PSW). And it was so steady. I think I recall He said It was nothing pathological, but an electric disturbance from the background. Does my description sound like such known electric disturbance from the background? What else could it be? And if it is an electric disturbance from the background – Does it have ANYTHING to do with the condition of one’s muscle (poorly relaxed for example) because it was normal straight line in the right triceps.

Answer

What you describe sounds like pure 60 Hz interference from nearby devices or a poorly attached ground. None of that is pathological, just electrical artifact.

Can EMG test flexibility?

Could anyone advice me if EMG can test flexibility and if so are there any references you could give me.

Answer 1

Certainly the muscle flexibility is important in sports and athletics. It generally would reduce injuries. In “routine” or the conventional EMG, we do not measure or test for muscle flexibility.

Answer 2

Routine EMGs cannot assess the flexibility of the muscles rather it is only a diagnostic tool. Flexibility is best measured clinically.

Answer 1

Certainly the muscle flexibility is important in sports and athletics. It generally would reduce injuries. In “routine” or the conventional EMG, we do not measure or test for muscle flexibility.

Answer 2

Routine EMGs cannot assess the flexibility of the muscles rather it is only a diagnostic tool. Flexibility is best measured clinically.

30-40% false negatives results in EMG

In your answer to a previous post you stated that some studies have indicated that needle EMG can give false negatives 30-40% of the time in detecting a root lesion. Why is this? Also does this apply strictly to testing for radiculopathies or other disease processes as well?

Answer

Yes, thanks for the clarification; the 30-40% false negatives in the studies I quoted applies only to radiculopathies. This is due to many factors, including the fact that while radiculopathies may be painful, they may actually not cause any nerve damage (which is what is picked up by the needle exam of the muscle), sampling or interpretation errors, detection error due to poor relaxation, timing of the exam etc..

Comment

Are there any general statistics in regard to false negatives or diagnostic accuracy in general for EMG? Or are there statistics for individual disease processes such as neuropathies, myopathies etc?

Answer 1

Well, generally speaking, in compression or entrapment neuropathies (such as Carpal Tunnel, Ulnar, Radial or Peroneal Neuropathies, or Bell’s Palsy), the yield is pretty high (I do not have numbers) even though there are still false negatives. In root lesions, as I mentioned before, the yield drops, as it does in neuropathies and myopathies, probably again in the 30-40% area. EMG is considered to have the highest yield in entrapment/compression neuropathies.

Answer 2

I would like to tackle this point by talking about how the electrodiagnosis contribution to diagnosis of myopathies in form of false positive or false negative. First of all, it is important to keep in mind, unfortunately, that none of the abnormalities in EMG is pathognomonic or specific for any single myopathic disease. Second, EMG is important but general guide to diagnosis, but we should keep in mind again that exceptions do occur. Now, the question, could EMG be false positive in myopathies? The answer is yes, due to technical reasons (MUP measurement, over-reading), also it can be false negative, due to again technical reasons (MUP measurement, simply missing mild changes) or mistaken the changes to be due other cause. Regarding neuropathy, again, false positive can occur due to technical reasons, temperature and age. While the false negative can also be due to some technical reasons in the recording.

Best time to perform EMG

My physician has referred me for an EMG. He has advised that I wait until I am symptomatic. I want to be sure I schedule it at the best time. My symptoms relapse and remit lasting for about a month with a two-month downtime between. I have: numbness and tingling in extremities, my knees buckle, vision disturbance, short bouts of tremor in arms, tightness in knuckles of fingers and toes, slight difficulties with fine motor skills in fingers–hesitancy, impaired balance. Last time, I even had a brief bout with facial paralysis (around my mouth) and difficulty swallowing. The visual and numbness/ tingling symptoms are the most constant, the others can last anywhere from a couple hours to 5 days. Which symptoms will assure the most thorough results from EMG testing?

Answer

The only time it makes a difference to be symptomatic or not for an EMG is when a doctor is suspecting diseases of neuromuscular transmission such as myasthenia gravis, because the findings do tend to vary. For other diagnosis such as peripheral neuropathy (causing the numbness or tingling) or entrapment or compression neuropathies, the general rule of thumb is that if you have a lesion there, it would be positive on EMG regardless of the timing of symptoms. So it is important to know what your doctor is suspecting before you decide to wait until symptomatic or not to have the study.

Comment

I think my doctor suspects a neuromuscular origin for my problems. Which symptoms (described earlier) would be most sensitive for testing? I.e. would a day with say vision disturbance, intermittent knee buckling and jerky pinky movements is a better day than just one with lots of tingling, balance and vision problems? If I am experiencing newer symptoms would they show up less than symptoms that have repeated?

Answer

Yes usually neuromuscular transmission problems manifest themselves primarily in visual disturbance (double vision or droopy eyelids) and fatigability. So the days that these symptoms are worse will probably be better days to be tested.

Comment

I am experiencing my 3rd month-long attack. Will older symptoms show up better than new ones?

Answer

Probably so.

Comment

It appears after doing some checking, that having an EMG + NCS while symptomatic will be logistically impossible because they cannot be scheduled on short enough notice. I have described my relapsing and remitting symptoms in previous posts. While I think my doctors would like to rule out problems of neuro-muscular origin, they lean much more toward CNS disorders at this time. I have difficulty believing that if I have this testing done while I am symptom-free and my nerves are functioning normally, that the EMG will be able to pick up the problem. How successful are the tests at recognizing difficulties like I’ve described?

How deep should the needle be insterted in EMG?

Is it important to insert the entire needle to the muscle?? The doctor who did my EMG told me that the active part is in the tip of the needle…

Answer

Enough part of the tip and the cannula need to be in the muscle to appropriately record the signal.

Sedation for infants during EMG NCV testing

My 16-month-old daughter was born with a left clubfoot, and bilateral PIP contractures of digits three and four. We were told she has distal arthrogryposis. The clubfoot did not correct completely with casting and bracing. She will be having surgery. The neurologist wants to rule out muscle and nerve disorders first. Can she be sedated for this test? Will the results be accurate?

Answer

Sedation, most often, is not needed for EMG because the test is tolerable and the muscle voluntary contraction is required which cannot be done under sedation. However, the doctor should be able to assess this need. The EMG in your child should give useful information about the status of the muscles and nerves.

Comment

Thank you for your reply. My daughter has a tremendous fear of doctors. In fact, we were unable to get x-rays of her foot, because she was so afraid of the technician and cried and climbed off the table etc…Therefore, knowing her, she won’t cooperate at all. I feel the only way is to sedate her. How much of the test will be reliable if I do? Will she wake up from the sedation when the electricity goes through, or when she feels the needles? Thanks!

Answer

Thank you for your email. Usually the doctors and technicians in EMG have their own kind way of dealing with patients from all ages, even infants. Therefore, I would not expect real difficulty during the test. However, the sedation does not affect the results of nerve stimulation. If she awakens during the test, it does not affect the result, even if there is a little pain or discomfort.

What is difference between acute and chronic? And does temperature effects NCV?

Results of my EMG/NCS – Right lower extremity Temp = 33.3C Conductions. Sensory conduction velocities at the lower end of normal, but within normal in the leg with normal amplitude. Motor conductions at the lower end of normal, but within normal with normal F-waves in the lower 60’s. – Needle exam Evidence of chronic low-grade denervation with increased numbers of polyphasic appearing units, but no significant giant units. Complex repetitive charges are noted in abductor hallucis and abductor digiti minimi pedis in both feet, and rare myokymia in abductor hallucis in right. No significant evidence of acute or chronic denervation is seen in more proximal musculature. Significant fasciculatory activity in seen in intrinsic foot muscles and in calf and anterior compartment muscles, slightly more prominent in the calf muscles than in the anterior compartment musculature. -Right upper extremity Temp= 33.6C Minimal slowing of sensory nerve conductions distally in the hand with conduction velocities in the low 40’s. Motor conductions in the upper extremity are normal with normal F-wave latencies. I’ve had fascics for, probably, 15 years. No weakness at all. Docs don’t have a clue except a diagnosis of a ‘neuropathic process with fasciculations and minimal nerve conduction abnormality, but needle exam findings suggest a very slow and indolent motor axonal process’. I think they are referring me a Boston NM expert. A couple questions….. 1) What is difference between ‘acute’ and ‘chronic’? 2) Were the temps in foot and hand low for this type of test? 3) I gather low temps can impact conduction velocities. Is it correct to assume that needle exam is relatively unaffected by temp. 4) Any of this look at familiar? They seem to think I was pretty unique.

Answer

In answer to your questions: 1) In needle exam terminology, acute means the presence of fibrillations and positive waves, usually indicating that the nerve injury is recent, more than 2 months and less than 2 years (these are approximations). Chronic means at least 6 months old (acute and chronic may coexist for a while) and indicates that the nerve has begun to regenerate and reinnervate the muscle. 2) The temps are within acceptable range 3) Generally speaking the needle exam is unaffected by temp except for fascics which may be decreased or altogether suppressed by low temps. 4) It is difficult to give an impression on the net. Findings such as yours can be seen in peripheral neuropathies. However such a diagnosis does not account for the fascics or the myokymias. I think a neuromuscular specialist who can put this together with the clinical symptoms would be of help.

Current Perception Threshold test

What is the current perception threshold test? Does it replace EMG

Answer 1

I am not quite sure what the Current Perception Threshold test is. It certainly does not replace an EMG. If you have more info on it, I would be happy to tell you more.

Answer 2

Perhaps this test is similar to the “Sensory Test” given at my medical institution. Ours involves testing for light touch, vibration and hot/cold sensitivity. I don’t believe that our testing includes any minimal electrical current perception, but I suppose this variation may exist.

Answer 3

I think as the name implies, this technique should be able to perform “non-invasive” and provides a kind of measure of sensory function using special surface probe. By all means as pointed out, it does not replace the nerve conduction or EMG studies.

Breathlessness encountered after EMG test

I would love to hear an opinion on a situation my mother recently encountered after having an EMG Test/NCT. She has had difficulty breathing since the day she had her test. This has continued for about one week now. She says she is experiencing “breathlessness”. It started the evening after the test. I would appreciate any feedback on this situation.

Answer

I am assuming that EMG/NCS was performed for extremity nerves. In this case the test by itself does not cause “breathlessness”. Therefore, my advice to see internist for her symptoms.

Comment

Thanks very much for responding. It was performed for persistent neck, back and leg pain.

Epileptic fits started after EMG test

I had a needle EMG to see if I had carpal tunnel syndrome and ulnar nerve entrapment, The test was very painful. I felt terrible shocks through out the test. I told the dr. how painful it was and he said we were almost done, well the last needle was inserted in the back of my head, very near the top of my spine, well the shock felt like I was being electrocuted. Immediately after that I was unable to speak without stuttering for at least one month. When it finally stopped my body was like having terrible convulsions. Finally that stopped and I started having seizures. Grand mal type. Now three years late I am diagnosed with epilepsy and I must take tegretol xr 6 times a day. What I need to know is if anyone heard of this happening before. I see a neurologist every 4 to 6 months and he said he doesn’t know. I never had seizures before this and they are not in my family also I didn’t sustain any other injury, except for getting my hand crushed months earlier. Please help me find out.

Answer

Seizures are caused by injuries (trauma, congenital, vascular etc..) to the central nervous system or can be due to metabolic disorders. EMGs come nowhere near any of the above and seizures are not known complications of an EMG exam. The timing of your episodes and the EMG exam is understandably curious, but the connection between the two can’t be made because of what I described above.

Is it necessary to move the needle inside the muscle during EMG exam?

I had needle EMG today. The Dr performing it, after every needle stick, moved the needle around roughly causing a lot of discomfort, is this something done with every stick; he also had me flex my foot when he was sticking my leg. I do understand that the nerve pain is at the insertion of the needle but to continually move the needle around after insertion, is that necessary. At times he scraped the needle back and forth after he inserted it, is this normal for this procedure. I thought when you are testing the activity of the muscle you have to have the needle still after insertion. I have had EMG before and it was nothing like this one. I ask the Dr. if I could see the results on the screen and he said he did not save any of it and showed me another pt’s results that was positive for nerve damage. He told me not to pursue nerve damage any further. Thank You

Answer

It is part of needle EMG to move the electrode inside the muscle, also to ask the patient to activate the muscle against resistance. This is quite normal procedure. However, the test is varies between the examiners and type of request for the test. However, the pain is short lasting and leaves no squeal.

EMG Procedure?

I am new to the world of EMG’s but have been ordered by my doctor to have one after an epidural went bad. How long do they normally take? Is there a physical before? Would I need to bring any information? How many needle insertions are normally in each leg, (which I am having done, lower leg nerve damage) and what other procedures are done along with it? I was freaked after the epidural went wrong, so this would all help to calm my fears.

Answer

The time of the EMG is variable depends on the patient but usually 30 minutes. You do not need to do physical activity before. The number of insertions again variable, the electromyographer decides that. The study consists of two parts, the nerve conduction studies, you would feel some electrical impulses stimulating the nerves causing movement of the muscle, it causes little but variable discomfort. Then the second part is the insertion of the needle electrode into the muscles (feeling of little prick). Both tests are put together to see whether your nerves are affected and how much. It is very useful and sensitive tests.

Thigh pain after EMG

I just had an EMG done, and ever since then, I have had some moderate to severe pain in my left thigh. I had no pain there before the test, which was quite painful. The doctor who performed the test doesn’t know why I would have this pain. Is this a common side effect of the EMG? If so, how long can I expect it to last? Any help you can give is greatly appreciated, and I look forward to hearing from you.

Answer

The pain or discomfort at the site of EMG insertion may last minutes and up to few hours and very rarely up to 24 hours. If it is longer or moderate to severe, another cause should be looked for. However, you did not mention how long you have this pain following EMG and why, to start with, EMG was performed?

EMG and Plaquenil

I am scheduled to have an EMG. I am currently on Plaquenil from a former doctor. The Rheumatologist told me to stop taking the Plaquenil because it could interfere with the EMG results. Is this true? I asked this question on the neurology forum and the doctor said they never heard of such a thing.

Answer

It is true that Plaquenil (Chloroquine) has neuromuscular side effects; muscular weakness or neuropathy, usually with long-term treatment, among other complications. The point, I do not know why EMG was requested?, perhaps, to check that this drug is not affecting your nervous system. If affecting, then you should discuss it with your doctor to discontinue or give alternative medication. Please update me if you wish.

I need some help to understand EMG Terminology

Can anyone help me interpret this: triceps has a mild increase in recruitment, amplitudes and 70% polyphagia. The only definition that I can find for “polyphagia” is food related eg. hungry. These segments are from my EMG. Thanks for any ideas or help.

Answer 1

Like any field in science, EMG has its own terms to describe the findings that tell us what kind of abnormality is there. First of all we use term polyphasia and not polyphagia (s not g). Polyphagia is related to eating, whereas, polyphasia (poly=many, phase=peak) means more than 4 phases of the EMG signal or response. Amplitude indicates the height of the response, either small or high compared to normal values. It is electrical term too. Recruitment is the way in which the muscle is responded to voluntary contraction. This term is derived from military, I think, to indicate a second line is moving to support the first line in defense. The muscle behaves likewise. However, the combination of these suggest either myopathic, neurogenic or of course a normal muscle.

Answer 2

Hard to answer your question without more details. What is your complaint? ie neck pain, injury… With a nerve injury, recruitment of motor units is typically decreased, which means you have fewer squirrels running the wheel. As we require our muscles to produce more and more strength, we “recruit” more and more units, faster and faster. If you don’t have the motor units left due to damage you end up with weakness in that muscle. Since you mentioned polyphasia and what I assume are large amplitude units, this indicates some level of reorganization of the damage is happening, which is a good thing. Again, this is a difficult question to answer without a little more info….

Why stimulation is repeated in nerve conduction velocity testing?

After placement of two skin electrodes on my forearm I received four “shocks” , each stronger than the previous. The location of these two electrodes was not changed during this. I asked the tech doing the test how much stronger I could expect the current to get & was told that it would get as strong as I “could take” & that electricity would be passed thru these same electrodes on the same site in increasing increments until I refused to take any more. Would you please tell me if this is standard practice for administering a nerve conduction velocity test?

Answer

I do these tests (26 years) and I’m afraid you were given a pretty feeble explanation of the execution of the testing. A nerve is made up of many tiny “fibers”, each of which is activated by a different strength of shock. The very first shocks you are given only activate a small part of the nerve. In order to have accurate testing, the ENTIRE nerve must be activated. This can require a rather large shock. It is common practice, though, to start at a low level of shock, and gradually build the strength up until the reading of the machine shows the technician that the whole nerve is activated (i.e.–the “bump” on the trace no longer gets bigger). Generally, shocks are given to one or two (but sometimes more) sites along any one nerve. Several nerves are done in this manner for the typical test. Patient’s reaction to these shocks is quite variable. Some cannot tolerate even the tiniest of the shocks, and I have had a patient or two SLEEP through the whole thing!! The average patient’s reaction is “I can put up with it for a little while, but I wouldn’t want to do it every day”.

EMG and Nerve Conduction report interpretation needed

Please help, Can anyone define and explain to me what this report means? EMG: This study provides electrical evidence to support mild chronic left L-5- S1 radiculopathy without acute on going denervation. Nerve Conduction: This study provides electrical evidence to support a left posterior tibial motor neuropathy with proximal involvement. The prolongation of the left H-reflex suggests an L5-S1 pathologic process.

Answer

Before I do interpretation. Please let me explain that EMG reading or interpretation depends generally on presence or absence of certain discharges (denervation activity), which usually suggest acute lesion in radiculopathy, and changes in the motor unit potentials, which helps to see the degree or duration of lesion. Therefore, if you have only motor unit changes of chronic nature without denervation activity, then this could explained that the lesion in chronic. The prolonged H reflex also supports that the lesion is in S1 distribution. I hope this is clear. I will be happy to help further if needed.

Curious about nerve conductive velocity test & EMG for ankle neuropathy

I am experiencing numbness, tingling in my right ankle and top of foot and big toe. My doctor has me set up for a Nerve Conductive Velocity Test and EMG on April 10. Can you tell me what to expect? Will the EMG just be done on the ankle area? My internist said my problems could be bone spurs in ankle or even some problem in spine. I am just wondering if test will cover spine too?

Answer

For more info on what to expect from EMG Nerve conductions, go to the EMG FAQ. The EMG will also explore problems originating from the spine as well, not just the ankle.

Comment

I just had my first NCV and EMG this week. I had reported a problem predominantly in the lower left leg. The NCV was performed on the left leg, front and back, but not the back itself. The EMG was performed on the leg AND the lower back. I suspect the EMG involved the spinal area since it’s the root of so many nerve problems. I’m also going for an MRI follow-up per the good doc’s recommendation.

What are normal motor units parameters (amplitude and Duration)?

What are the normal ranges for the amplitude and duration of normal healthy motor units?

Answer

The duration of the MUP is typically between 5-15 msec and is generally affected by several factors, number of muscle fibers in the motor unit and how do they fire (depolarize), muscle by itself, age of the subject and temperature. While the amplitude of MUP is again variable but greater than 100 uV but usually less than 2 mV, but be careful, It varies depending on how close the needle is to the motor unit, number of muscle fibers in the motor unit, their diameter and way of firing.

Drugs before the EMG test to calm / pain reduction?

What about Valium / Xanax / or others before the test to calm the patient who has a driver???? I am rather needle phobic (though getting less each test) If a drug will help me feel better about the test and will not interfere with the test results than I would like some feedback. I am currently taking Vicadin and Oxyctin 10(at night time only). Anything with the word “NEEDLE” freaks me out. Sticking me multiple times, and leaving it in seems worse. Though many have told me that the EMG is not pleasant but bearable I still would like to know about possible med’s for scary cats like me.

Answer

Although EMGers utilizes needle electrodes, in majority it is well tolerated. However, an analgesic may be used in some cases. It is up to the treating doctor to order it, according to the patient’s condition. It does not interfere with the EMG test.

EMG and EKG are they similar?

I would love to hear an opinion on a situation my mother recently encountered after having an EMG Test/NCT. She has had difficulty breathing since the day she had her test. This has continued for about one week now. She says she is experiencing “breathlessness”. It started the evening after the test. I would appreciate any feedback on this situation.

Answer

Can a EKG be used similar to a EMG? My doctor had me sit for EKG test, and then he dropped the leg portion so that my legs were dangling. He then did a EKG. When I questioned him as to why, he mumbled something about the feet. I am totally baffled as to what a EKG has to do with my heart and feet and the severe spinal stenosis that I have.

Can muscular tension affects discovery of signs of denervation?

I know that tension in the muscles can cause spontaneous activity (fasciculations), but what about fibrillations? Can muscular tension cause them also? (Because they represent muscles fibers which lost their primary innervation)

Answer

The spontaneous activity needs a relaxed muscle to be recognized. Therefore, muscle activity or “tension” either voluntary or involuntarily would interfere with proper identification of spontaneous activity being fasciculation or fibrillation.

Stability of MUP and significance of spike duration and rise time

What are the parameters for motor unit stability? What is the significance of the spike duration and rise time? Does it have something to do with measuring stability?

Answer

The MUP stability is determined by the shape of MUP waveform. Normally, the MUP waveform does not change with firing or discharge. When components of the waveform is changeable; fire earlier or later or even disappear, they result in an unstable MUP. It occurs in processes of neurogenic or myopathic lesions. The duration and rise time are parameters used in quantitative measurement of MUP not for stability.

Comment

So what is the significance of spike duration and rise time in neurogenic process? Would they be increased?

Answer

The duration is increased in neurogenic process, but the rise time is used in neurogenic lesions, but only to determine whether the MUP should included for measurement or not.

Comment

What is the difference between the spike duration and the “duration” of MUP? ARE THEY BOTH PROLONGED IN NEUROGENIC PROCESS?

Answer

Strictly speaking the term spike is used commonly in electroencephalography rather than EMG. The term Spike is a wave of short duration. But in EMG we usually and practically refer to the duration of MUP, which is increased in neurogenic process. Spike duration is the duration of the major spike component of the MUP.

Motor unit changes with advancing age

I read in several textbooks that motor units size vary quite significantly with age. Yet I never could understand how does it vary? Are the motor units getting larger or smaller with age (by amplitude and duration)?? , Would we found smaller or larger motor units in old people, comparing with young people My understanding is that as people get older, they lose muscle bulk and that loss is more significant than any loss of anterior horn cells, so as we get older, there are less muscle fibers with relatively the same amount of anterior horn cells, so each motor unit contains less muscle fibers and therefore gets smaller on average, as we get older. This is my assumption, never read it …

Answer

Where you’re getting confused is with the relationship between muscle bulk and motor unit size. A muscle can be atrophic and have large motor units. The reason for that is that with the loss of anterior horn cells with age, the anterior horn cells, which remain, take over the territory (ies) of those which have died resulting in larger motor units. Because they may not be able to take over all the denervated muscle fibers, the muscle, in total, still has a positive loss in the number of innervated muscle fibers and may atrophy while those motor units inside of it that have survived are actually larger than normal.

Comment

You mentioned the loss of anterior horn cells with age.. I thought that muscle fibers actually degenerate also (without respect to the anterior horn cells, the same as all body tissues degenerate -skin, cartilage….) and I thought that the loss of muscle fibers is more prominent than the loss of anterior horn cells… The question is: IN the old… does the EMG get “neurogenic” (large amplitude and duration…., with fewer motor units, due to loss of anterior horn cells) or “myopathic” (small motor units, due to loss of muscle fibers)? Which is more prominent: THE LOSS OF MUSCLE FIBERS OR THE LOSS OF ANTERIOR HORN CELLS AS WE GET OLDER according to your experience with older and younger patients

Answer

The EMG tends to get more neurogenic with age

Question about normal values for peroneal and tibial nerves latency. Also what about safety?

What would be normal values for peroneal and tibial nerves (latency in ankle, motor amplitude…)

Answer

Peroneal nerve values: Terminal Latency: 2.6-6.2 ms Amplitude: 2.6-20.0 mV Motor velocity: 42.9-55.0 m/sec. Tibial nerve values: Terminal Latency: 3.0-6.1 ms Amplitude: 5.8-32.0 mV Motor velocity: 40.0 -62.1 m/sec All the best.

Comment

I wanted to ask about THE EMG safety also… what is the amount of electric stimulations (the maximal) you give in EMG? (in Ampere) I read somewhere it is 10-75 MA WHICH AMAZED ME AS I KNOW A CURRENT OF 30 MA is enough to kill a person!!! So how come it is safe?? (May be it is micro Ampere rather than Milli Ampere???) Also, Does the electricity you give really travels through our body or it just the sensory stimulation (natural) that travels? Are there any web site with information on EMG SAFETY

Answer

Thank you for this point. It is important issue. Your numbers are correct, in mA (maximum 100 mA), not MicroA. The point is that this amount of stimulation is given for very brief period range from 0.05-1.0 milliseconds only. There are always safety regulations and no EMG machine is approved unless it fulfills all safety rules by law. The patient safety is always on the top. Regarding the electricity, it travels only through the nerve under study. For the web sites, I am sure there are web sites for EMG Safety but I do not recall or have any at present.

Comment

About the safety… Do you know of any researches about the long term effects of an EMG test (the “electric part”) such as possible nerve problems, cardiac problems (that show up after long time) etc… For example with people who had several EMGs over the years? Do you know of any short-term hazards? (Such as people who feel bad or faint right after the EMG? * I read somewhere that increased exposure to electric shocks has been linked to a variety of fatal disorders such ALS and renal cancer… (That is why pilots get more ALS and RENAL CANCER according to this research…)

Answer

I am not aware myself and I did not read about any long term effects of our “diagnostic” nerve stimulation electrical tests, even if several tests are performed per year for a normal person or patient in child or adult, female or male, animals or human. For short term, talking usually about minutes, pain (variable between persons), usually tolerable. I have not seen a person fainted from nerve stimulation tests. The final point, I am not sure what sort of electrical shocks and for how long the exposure to be linked to fatal disorders. It would be interesting if I can read this article.

Comment

here is the article…. Electric shocks linked to Gehrig’s disease August 18, 1998 NEW YORK, Aug 18 (Reuters) — A study of utility company employees in Denmark suggests a link between amyotrophic lateral sclerosis (ALS) and exposure to electromagnetic fields or electric shocks, according to a study published in the August issue of the American Journal of Epidemiology. ALS — also known as Lou Gehrig’s disease — is a rare, fatal disease characterized by weakness and atrophy of muscles and a degeneration of the nerves that transmit messages to muscles in the brain and spinal cord. In the study, Drs. Christoffer Johansen and Jorgen H. Olsen with the Danish Cancer Society in Copenhagen examined National Death Certificate files for the cause of death in 21,236 men employed in 99 utility companies in Denmark between 1900 and 1993. Medical records were obtained to determine cases of ALS. Overall, 3,540 deaths were noted in these workers, slightly fewer than the 3,709 expected based on national mortality rates. Analysis of the records revealed a twofold increase in deaths from ALS in these men and a tenfold increase in deaths from electrical accidents on the basis of 14 and 10 deaths, respectively. Death from ALS was also found to increase with time since first employment in a utility company. “The excess mortality from amyotrophic lateral sclerosis seems to be associated with above-average levels of exposure to electromagnetic fields and may be due to repeated episodes with electric shocks,” the authors write. However, the study did not find that increased rates of other neurological conditions such as senile dementia and Alzheimer’s disease in these men, nor an increased risk of suicide. Previous studies have linked these conditions and suicide to above-average exposures to electromagnetic fields. “The pattern of mortality from ALS, however, suggests an association within jobs entailing medium to high exposure to 50-Hz EMFs (electromagnetic fields), possibly due to an increased number of episodes with electric shocks,” the authors conclude. —————————————————————- So what is your opinion on that Doctor? Is there a great difference between the electric shocks they mention there and the electric shocks in EMG?

Answer

I am sorry for being late in reply. I will not discuss whether the relation is proven or not, but I want to say this kind of electrical exposure (EMF) is different from that used in field of nerve conduction studies. The exposure, however, in nerve stimulation is low and very brief indeed.

Motor unit changes with aging.

I was just wondering after attending a neurobiology lecture what happens to motor units in muscle as people get older? Do they just decrease without use or stay the same?

Answer

Aging brings about a decrease in the number of motor neurons in the spinal cord. Given that a motor neuron with its axon and all the muscle fibers it innervates is traditionally referred to as the “motor unit”, there is a drop-off in the number of motor units with aging. Motor units which survive begin taking over the muscle fibers of those which lost their motor neurons and therefore the surviving motor units increase in size. So with aging you have a combination of a drop-off of motor units and an increase in size of the surviving ones.

Is EMG test painful?

Can anyone help me interpret this: triceps has a mild increase in recruitment, amplitudes and 70% polyphagia. The only definition that I can find for “polyphagia” is food related eg. hungry. These segments are from my EMG. Thanks for any ideas or help.

Answer

I am scheduled for an EMG on Wednesday the 11th. They are looking at my neck. I was rear ended in an accident and this caused a disc to protrude and touch my spinal cord. I have been having trouble with weakness and numbing in my left arm. I’m a little nervous (also, I’m a wimp) and would like to know if it is painful. Thank you in advance. In conclusion, I wanted to know if the EMG was painful (not the neck injury).

Comment

Thank you for responding. I went through the test and it was quite tolerable. A couple of times I had pain, but mainly that was the needle. Thank you again.

Comment from another Patient

I am quite upset. I just had an EMG today performed by my doctor’s associate….another doctor. He briefly explained the test. He did explain the first part about the electric current, etc., which was uncomfortable, tolerable. However, he then proceeded to unwrap a needle. I asked if it would hurt, he said “no…I’m just going to listen to changes in sound waves of the nerve.” I must have asked him three times if he was going to keep sticking me with that needle and he said “no.” But, as you know, he did stick me several times in my left and right arm…performed the test quickly, and I feel haphazardly. Two of the spots where he inserted the needle bled a lot and became swollen. (A hematoma, I think.) He wants me to go back for a test of my spine, which I don’t want to do. I have 2 bruises and want to know how common this is with this test. I am duly upset because of his not being honest, him hurting me, and the bruises. Thanks for your feedback.

Comment from another Patient

I had an EMG and NCV about two weeks ago. The NCV was, to me, worse than the EMG, yet even the NCV itself wasn’t that bad. I certainly do NOT dread my next EMG. There’s just a minor pain at insertion, which I found less irritating than, for example, the needle prick associated w/ giving blood.

Comment

Thank you so much for responding. Yes, I do have to agree that it was the needle that caused the most pain, but I got through it just fine. Thank you again.

Leg is worse after EMG test done for hypokalemic periodic paralysis

My 14-year-old daughter was hospitalized a month ago after experiencing paralysis in her arms and legs. A pediatric neurologist determined that she suffered from a condition known as hypokalemic periodic paralysis. An EMG was performed the first night in the hospital, which confirmed the doctor’s suspicions. An MRI, EEG, EKG and a pulmonary function test were also done to rule out anything else. Her arm function came back by the end of the first evening in the hospital. However, her legs came back a little slower. Her right leg came back suddenly three days later, however her left leg did not come back for another three days but the function came back floppy weak and painful to walk on. The neurologist scheduled another EMG five days later to again test her muscle function. Although the first test was three hours long and quite uncomfortable for my daughter, she was able to endure the pain. However, the second test was so agonizing with excruciating pain that my daughter was unable to complete the test. She only lasted about 30 minutes until it was so unbearable she could not breathe. After that second test, her left leg was worse with extreme pain. It has been almost a month now and it has not gotten any better and she is unable to bear her weight on it without pain. Could the doctor have damaged her sciatic nerve? The pain is from her hip all the way down her leg. She is on Diamox and Potassium to treat the hypokalemia. The other symptoms she had been having prior to being diagnosed with hypokalemia have disappeared (body pain and fatigue, insomnia, headaches and muscle and bladder spasms) except for this leg problem. She is receiving physical therapy twice a week and the therapist is as baffled as we are to why is not getting better. Please advise.

Answer

Nerve conduction studies and EMG are useful to diagnose hypokalemic periodic paralysis during the attack. This should reverse back to normal between the attacks. But, I am not aware of any case got sciatic nerve injury during such procedure. Please consult a neurologist to verify the problem.

Help w/ Interpretation of EMG Results please is it really poor

Can somebody help me interrupt the following EMG results? “Mild denervation potentials were identified in the left tibialis anterior alone. Changes of denervation with reinnervation were seen in the tibialis anterior and EDB.” Also: MUAP L. TIB ANTERIOR Amplitude: Few+ L. EXT DIG BREVIS Amplitude: Few +, Polyphasia Few + RECRUITMENT L. EXT DIG BREVIS Pattern: – (minus sign)

Answer

EMG interpretation is best left to professionals who have performed the test and should give you an impression and interpretation of what they found. It is best to have your doctor explain it to you.

Comment

The sad part is this impression was likely written by his physician. Poor reporting.

Answer

That’s possible in which case it is not an adequate report, and it is certainly incomplete.

Variation in normal EMG

My daughter age 19 had an EMG today due to a cervical spine injury 2 years ago. MRI shows minimal bulge at C4-5, 5-6, spur at C2 and an annular tear HIZ at c 5-6. She has complained of pain in her neck, shoulders, and right arm with numbness and tingling of her right 3rd, 4th, and 5th fingers. The EMG was read as normal but in looking at the numbers there was variation in the conduction velocity in her arms. Right Median 56.5 Left median 57.5 Right ulnar-elbow to wrist 64.4 Left ulnar-elbow to wrist 59.2 Right ulnar-across elbow 65.4 Left ulnar-across elbow 58.7 I understand these are normal ranges but should there be this much difference between right and left or could this be an indication of some early damage? She believes that the pain and sensory deficits are getting worse. On physical exam she has hyper-reflexia of her upper extremities and bilateral positive Hoffman’s sign. The neurologist that did her EMG today said that she may have had some bruising of the cord resulting in these symptoms of cord compression. Thanks in advance for any information you can give me.

Answer

These values are still normal. The variation does not indicate damage in this case. You see, the difference has to reach certain value such as 15 m/s, to be significant or by itself reach lower certain values. However, the treating doctor always would take the findings within the clinical context.

Curious about EMG testing in CTS

My Doctor wants me to have an EMG test. I have carpal tunnel syndrome in both hands. I’ve heard it’s very painful and many times not 100% accurate. Is the test very painful? and how accurate are they? Is there a surface test that can be done that’s less painful and just as accurate? Please answer my questions as this test just around the corner for me, and I’m scared. Thank You

Answer

The study is divided into 2 parts; the nerve conduction studies, NCS, (surface test, no needle), where there is little electric shocks to study the nerves. The other part consists of inserting electrode (needle) in the muscle, little distance and it would induce little discomfort and pain. This pain is quite variable between individuals, but in vast majority both tests are tolerable and no squeal. It is important to do in patients with carpal tunnel syndrome (CTS). It is highly sensitive and accurate in CTS. I would, personally, say more than 90% (scientifically difficult to say 100%). Now, it is up to the examiner to perform both tests or would get away with the nerve conduction without the needle part. Actually, not every patient with CTS needs the needle part. It depends mainly on the patient’s symptoms and signs, and obviously, on the obtained results of NCS, as well.

Please don’t take Offense at this question! Can EMG be Rigged?

What about Valium / Xanax / or others before the test to calm the patient who has a driver???? I am rather needle phobic (though getting less each test) If a drug will help me feel better about the test and will not interfere with the test results than I would like some feedback. I am currently taking Vicadin and Oxyctin 10(at night time only). Anything with the word “NEEDLE” freaks me out. Sticking me multiple times, and leaving it in seems worse. Though many have told me that the EMG is not pleasant but bearable I still would like to know about possible med’s for scary cats like me.

Answer

First of all; I do accept your question, no offense, it is nice interesting question. Now, back to question, EMG and nerve conduction studies are done under strict internationally controlled criteria, similar to operating computer or driving a car. You must follow rules. In our field, therefore, EMG and nerve conduction studies follow 2 lines: one is technical which cannot be rigged; we go by numbers and parameters. Having said that, we should always know that these studies have limitations and can be normal even if the patient has symptoms. This brings me to the second line, the interpretation part. Here the doctor explains the findings and then would attempt put data or findings together for certain disorder and to correlate the findings with the patient symptoms. Here, comes the experience of the examiner and “tailoring or rigging”, but do not get me wrong, even here we follow rules of medicine in interpretation but of course depends on experience and knowledge of examiner in putting the data together and considering some findings as significant or not. That is why, in our reports we always have the technical data are written down for the referring doctor to see, followed by examiner report and interpretation, this may vary but usually well agreed upon. You see we do, with God help, our best for the patient care. Regarding your other point, EMG can be normal if you have tingling in both little fingers. EMG is useful to diagnose a lesion of the nerve itself or radicular lesion. But, if due to central lesion (spinal cord or brain), then EMG does not help, other radiological evaluation is needed, but it is up to treating doctor.

Comment

Hello. Could you provide reference to the criteria which you refer to – i.e. what is the governing organization or standard? And is there a web site? Also, is there a type of EMG which does not have any numbers of a graph associated with it- and if so when would this be the case. Thanks

Answer

The website of American Association of Electrodiagnostic Medicine is useful: www.aaem.net, especially go to practice parameters (http://www.aaem.net/practice_parameters.htm) or (http://www.aaem.net/publications/ practiceaids.html#Guidelines%20in%20Electrodiagnostic%20Medicine). Regarding your last point, I am not aware of EMG without numbers or graph.

Comment

I am thinking those machines are messed up also cause I have severe pain and numbness in my right leg and foot and they said that everything showed normal but I told them that something isnt normal.

In need to understand some terms in NCV report for CTS

I have had a nerve conduction study of the upper extremities: revealed prolonged terminal latencies of the Rt. median motor, sensory, midpalmer bilaterally; left mid sensory mildly prolonged as well. Abnormal nerve conduction exam of both upper extremities are suggestive of focal median nerve entrapment neuropathy across the wrist (CTS) bilaterally, Rt. > left. I have yet to actually see the neurologist, appt set up; however in the mean time, what’s the translation of terminal latencies prolonged, abnormal exam. What is a large fiber diffuse peripheral neuropathy, (states no evidence of). The only repetitive motion I have in my life is 6-8 hours (intermittently) on my job, I case and deliver mail. I have filed wc/occupational illness. I had the NCS done before filing so to have proof of condition. Talk to me someone! I am in braces 24/7 weight limit 15lbs lifting until owcp gives an answer. I’m concerned…surely my job duties has caused this, right? Intimidation is not a pleasant experience.

Answer

To be precise and go to the first point, “the terminal latency prolonged” means that, there is pressure or entrapment of the median nerve causing slow of conduction or response on electrical stimulation of the nerve. The second point, “large fiber diffuses peripheral neuropathy”; there are 2 kinds of nerve fibers; small and large nerve fibers. The usual nerve conduction studies deal only with large nerve fibers. Therefore, when those nerve conductions are abnormal, then we refer to large fiber affection. Now, the last point. The CTS is very common condition all over the world. It is related to repetitive actions. Thus, it can be an occupational illness.

Comment

Thank you so very much for the response. This is about all the response I can muster right now.

EMG Technique (description)

I am scheduled for an EMG Test after some concerns were noted in my nerve conduction test in the upper extremities. Could someone explain his experiences with the test? Painful? How long does it take? In general, what can I expect? Thanks.

Answer

The needle EMG part of the test consists of inserting needle probes in the muscles, usually, 4-5 such insertions per extremity. No electrical currents are delivered by the needle, no blood is drawn and nothing injected; just a sampling of the muscle to see if it is normal or not. Though the sticks are less painful than injections, they are nevertheless uncomfortable. One extremity needle testing takes about 10-15 minutes and usually reveals very useful information about the nerves and muscles.

EMG Technique (use in determination of injury duration)

Can an EMG and nerve conduction test tell if nerve damage is from an old injury or a new injury?

Answer

Yes, the needle part of the test can usually tell whether an abnormality is from an old injury or a recent one (under 6 months old)

Heat role in EMG results

I was given an EMG test, the doctor did not like the results of the test. So he placed heating pads on both of my hands/wrists/arms for about 10 minutes & re-took the test, right side first. I passed on the right side but again failed on the left. So he heated me left side up again & I passed. Is this a normal procedure to heat up the arms & etc. I was not cold nor cold to the touch? What is the reasoning behind the heating procedure if it is normal?

Answer

The change in temperature can affect the nerve conduction studies to great deal even in normal persons; the cold (even if you do not feel it) can cause slowing in nerve conduction. Therefore, it is important to check the temperature (skin temperature) before, during the test or at least in case of slow nerve conduction.

Practical use of EMG in trauma

Can an EMG and NCS differentiate when an injury actually occurred? I would like to email someone to discuss this more

Answer

Yes, EMG and NCS studies are helpful in nerve injuries, for instance after trauma

Nerve injury due to bulged disc; is it reversible?

If a disc has caused nerve damage in an arm, will it be permanent or can it be fixed?

Answer

Nerve damage is reversible when the nerve is still connected (in continuity) and the cause of the damage has been removed. Disc bulges usually leave the nerve connected, so when the cause is eliminated (or gets better on its own) the nerve regenerates. Nerve Growth is slow though, about 1 mm/day.

Mixed median nerve neuropathy with demyelinating features

I was tested two years ago and just advised today that I have the above diagnosis. I would like more information as I was told there is nothing to do since the damage has been done, except pain control and seeing a neurologist. Where do I find out more about this?

Answer

That does not sound like a very good EMG diagnosis because it doesn’t tell you much. Usually demyelinating lesions of the peripheral nerves heal very quickly, unlike axonal lesions, where the nerve fiber is cut, which take longer to heal. I would have that report looked at by a qualified EMGer, neurologist or physiatrist

Increased insertional activity

How does increased insertional activity sounds like? (The one, which is seen early in the course of denervation)? Does it sound different than cramps – poorly relaxed muscle?

Answer

That’s a tough one to describe in words, but basically what I call increased insertional activity is when I begin to see insertional potentials (and I am away from an end-plate zone) which look like fibs and positive waves but which never become spontaneous and persist after I stop the insertion. The sound is a bit similar to a brief end-plate zone noise, which does not persist. It is a much “quieter” sound than that of a cramp or a poorly relaxed muscle.

Comment

Hi! Thank you for your elaborated answer. I know that a cramp (or poorly relaxed muscle) sounds like a high frequency, repetitive bursts very very very fast (like a machine gun fire)-does increased insertional activity SOUNDS also like that?

Answer

No, nothing like a cramp, much quieter.

Normal EMG in a complaining patient

Well I had my EMG done and it wasn’t too painful but they didn’t find anything in it so they really don’t know what’s wrong with me. My orthopedic now suggests physical therapy. This is driving me crazy I’ve had this injury since November. I just want to know what’s wrong with me.

Answer

An EMG can still be negative and you may still have a pinched nerve. But in situation like yours the pain may also be musculo-skeletal in nature, that means from muscle spasm, local joint inflammation or a sprain. If Physical Therapy doesn’t help, an MRI of the spine would be useful to make sure there is no pinched nerve.

Nerve damage healing process

Upon your advice, I went to see a neurologist and had an EMG. The doctor told me that I had nerve damage due to the three surgeries I had in October. He said that the nerves would eventually regenerate and gave me a prescription for amitriptyline. He wants me to work up to 50mg daily. Right now I am up to 40 mg. I notice a very slight improvement in the pain, burning, numbness, etc. Can you tell me how long the nerves could take to repair themselves? Am I looking at possibly a year or even more? It is the nerve that runs from the groin down both sides of the thigh and across the knee. Thanks for your comments.

Answer

Nerves grow very slowly, about 1mm/day, you can almost compare it to how fast a hair grows and you will have a ballpark figure. So it takes usually anywhere from 6 to 18 months. Amitryptilline and other drugs like it help relieve nerve pain such as yours so this should help and you should start noticing some improvements.

CMAP question

I know that in MND\ALS the CMAP are normal initially, later it is abnormally low. my question is: in VERY early denervation, there are many new motor units – that were formed to compensate the loss. So, is it possible that in the very early phase of denervation, the CMAP (which is the measure of number of motor units) will be slightly pathologically higher – I mean for example that the affected leg would have higher CMAP than the non-affected one? I relate to the very FIRST WEEKS OR DAYS OF DENERVATION

Answer

In early denervation, there are no newly formed units, there are surviving units who take over muscle fibers from the units which were denervated from the loss of their axons. If the reinnervation is adequate, most denervated muscle fibers are reinnervated in this fashion, but the total number of muscle fibers in the muscle remains the same so the actual size of the CMAP does not change. The CMAP size decreases only when enough muscle fibers are denervated and cannot find surviving units to take them over.

EMG electrode needle

HI Does the size and type of a needle used during an EMG can affect the number of motor units which are recruited. (Does a fine needle recruits less mups in a MAXIMAL effort)??

Answer

Two things the size of the needle does with smaller electrodes: 1) It has a smaller pick-up area, therefore you see less muscle fibers 2) The amplitude of the action potential drops much faster when you move the needle electrode, so unless you’re real close to the muscle fibers in your pick-up area, you don’t see them very well. You will have small rounded potentials.

Comment

What did you mean by less muscle fiber seen? During exertion, more and more motor units appear, until there is a full interference pattern – If you use a very fine needle does it take more time to get the full interference pattern???

Answer

Think of an electrode as a microphone and the muscle fibers as musical instruments. If you have a small, highly selective microphone, which you put in front of the solo violin, you will only hear the sound coming from that violin and very little else. Whereas if you have a large fairly non-selective microphone which you hang high above the orchestra you will capture the sounds of many more instruments, although not as “faithfully” as the small selective microphone real close to the violin. So large sees more (or hears more) and small sees less.

Comment

You mentioned that the bigger the needle is, the more fibers it collects: what about motor units -1. Are more motor units recruited with larger needle? so does it take more time to reach the full interference pattern with the smallest and finest needle? 2.Does the needle picks up motor units from neighboring muscles or just from the muscle where the needle is??? I mean: is it possible that the muscle where the needle is placed is dead (all the motor units are dead) and the needle will pick up motor units from neighboring muscles in exertion? (Which will make hard to know the condition of this specific muscle) THANKS FOR READING THIS POST

Answer

Replies to your post: 1. No motor units are recruited by the nervous system in response to a demand for increased effort so needle size has nothing to do with it. 2. No the needle electrode picks up motor units only for the muscle it is in.

Comment

This is sort of an interesting issue and the discussion has raised several questions in my mind. I have read about how the MUP drops off significantly as it’s distance from the needle increases. When you do an insertion and sample in a given direction, how many MU are studied (spontaneous or voluntary activity) in that position? I realize this depends a lot on the size of the units, density, etc. so lets say a muscle with a large number of MU such as the bicep. And in a related question when sampling in multiple directions how big of a “radius” is studied from that one skin insertion point. Thanks again for your kind help. Regards,

Answer

Muscles fibers compose the MUP. Each MUP reflects about 15 muscle fibers or less depending how close to electrode. In routine EMG needle examination (nearly always we speak about it in this site), the size of the needle whether thin, thick, short or long, all have similar action and function. Interference pattern or pick up area is the same whether short or long needle, because the recording surface is the same (conventional EMG needle electrodes), which is used in most clinical examinations, called concentric needle electrodes. The other point; the muscle is recognized by its anatomy. The experience of the examiner is important in this aspect. If the muscle is atrophic or fibrosed (dead motor units), you may record MUP from nearby muscles. These are identified, as they are distant and low in amplitude. So these are not taken into account. I hope this answered your queries.

Fibrillations

Hi upon the insertion of the needle in my EMG a few weeks ago there were popping sounds that lasted until I activated this muscle (exertion) the popping sounds last for quite long time in a rather rhythmic way It was pop pop pop pop pop pop pop pop… in a very regular way until exertion and then they stopped they were not slow but they were neither very fast. I asked the doctor if these were fibrillations and he said “no, relax your muscle” how could he be so sure?? Does it sound like fibrillation? Do fibrillations fire with long intervals? Are they rhythmic? DO they last for long time? And most important: does it sound like a POP POP POP or more like a brief BIP – bip or pop??..

Answer

It is usually easy for electromyographer to recognize whether fibrillation or not is seen by needle EMG. When he asked you to relax, it means that it was likely to be voluntary motor unit firing and not fibrillation. To come back to your point about fibrillation; each single fibrillation fire regularly (rhythmic) and has initial (down going) positive deflection. However if many fibrillations fire at the same time it would sound like irregular firing because their firing rates are different. I believe the best description for fibrillation sounds like “raindrops on tin roof”. Its frequency is usually close to 10 Hz. It has short duration less tha 3 ms.

Comment

You mentioned: raindrops on tin roof: 1.does it fire in equal intervals? Like tu-tu-tu-tu 2.how long does it last from the moment the needle is in: does it start and stop and start. 3.and again about the sound: does it have a relatively thick sound (tu-tu-tu-tu..) or like a bip?

Answer

Hi, yes it fires usually regularly at fixed intervals. It lasts for variable interval. They vary in abundance, from few to profuse everywhere for variable period. Regarding the sound, only I tried to make it easier to appreciate the sound, but you may have never heard raindrops on tin roof or crinkling cellophane. Therefore, we should consider other features of fibrillation in addition to sound. I hope this will help.

Comment

Does it sound like 1. a tap that has been left opened and its drops hit the washbasin rhythmically-drop by drop: tip tip tip tip 2. Or more like a sound of rain drops – many of them that you cannot distinguish by sound each one of them (of the many rhythms) – because there are many rhythms as you mentioned – so you get irregular sound my questions refer only to the sound produced by the EMG – regular and rhythmic or not? THANKS IN ADVANCE!

Answer

OK. It is similar to pattern 2. Many fibrillations (commonly) fire at same time, sound like irregular firing.

Comment

How would you define the SOUND of fibrillation seen in an EMG? What sound is made according to your experience?

Answer

Have been following the discussion thread. All I can tell you is that learning to distinguish fibrillation potentials from other activities by EMG is fairly simple and straightforward and one of the first things EMGer learns, so I would trust your doctor’s judgment on that.

EMG/NCV test

I have to go for an EMG/NCV test. What are these tests and how are they done? Are they painful? Are they long test? I have swelling of the wrist and a lot of pain in moving it, also numbness in hand.

Answer 1

The test is uncomfortable. The word is not really painful, but somewhat unpleasant. It is very necessary and can prevent a miss-diagnose. I didn’t realize that a nerve up in your neck could make pain in your hands then wrist, and arm. My neck doesn’t hurt or isn’t stiff. But I was given a cortisone shot for Carpal Tunnel when I didn’t have CT. so GO FOR THE TEST.

Answer 2

The test usually takes anywhere from half an hour to 45 minutes. Though uncomfortable it will be useful for you to find out what the problem is.

Can EMG determine if the nerve injury is old or new?

If a person has symptoms of nerve damage or entrapment but EMG (3 separate tests) shows no nerve damage, then 6 years later after an accident develop the same symptoms but much worse and EMG is positive. Can tests prove that the damage came from the most recent injury? And what would have made the person have those symptoms without tests being positive with the first accident?

Answer

I don’t know why the EMGs were negative 6 years ago but the answer to your question is that yes, EMGs can usually determine if a lesion is over 6 months old or not.

EMG “insertional activity”

First, I would like you to know that I as well as many other patients appreciate the fact you are sharing so much productive information with us! My question is that: according to medical textbooks a normal resting muscle is electrically silent. However, from what I have read in this forum and told by my neuro, It is quite common to have “a noisy insertion” – what so called benign conditions “create” benign insertional activity in rest that also have a “WAVE FORM” (by wave I mean the morphologic wave such as fasics, fibs, and positive waves but a benign wave? what are the benign activities which have a wave form that MORPHLOGICALLY may look like fibrillations?

Answer

Hi Bobby. What you’re describing refers to end-plate noise, which is the activity generated by the muscle when the needle is inserted near the point where the nerve enters that muscle. You can read up on it at: https://www.teleemg.com/jbr110.htm where you can get a good description.

Comment

Thank you for your thorough reply! What about cramps/poorly relaxed muscle – Don’t they also “create” benign waves? Is it possible for voluntary units to fire during rest? (And then again we have “benign waves”)

Answer

Cramps or poorly relaxed muscle don’t sound anything like the end-plate noise I described above. hey look like regular motor units, which is what they are. Normally voluntary motor units do not fire in a fully relaxed (uncramped) muscle. Voluntary units firing at rest are called fasciculation potentials.

EMG Results in sensory polyneuropathy

I apologize for the length, but I wanted to be sure I present the pertinent info. I have been having problems with numbness and tingling in my hands and feet/legs. My back feels fine-no pain, great range of motion, with mild sciatic pain on occasion with certain movements. 12 years ago I had a lumbar laminectomy, which was quite successful. Recent MRIs and X-Rays of my cervical region were completely negative, as was brain MRI. MRI of lumbar showed marked narrowing of the L5-S1 space with a few mildly bulging discs. No evidence of nerve impingement. Neurosurgeon thought my lumbar spine was not causing the problem. Had EMG/NCS on a left arm. EMG was normal, however NCS was not. Left ulnar sensory was unobtainable. Left Median sensory was not normal although not absent. When the neuro did the leg, following the arm he did not do the EMG. Only NCS. Sural was unobtainable. (I could tell something was wrong during the test, because in certain areas when he jolted me, I could not feel a thing, or felt a lessened response. I have had previous tests years ago and could definitely feel it). The interpretation was as follows: This is an abnormal nerve conduction study due to low amplitude in the left median sensory and marked slowing of nerve conduction velocity, absent ulnar sensory and absent sural. This is consistent with a sensory neuropathy, apparently both axonal and demyelinating. The results were reviewed by several other neuros who agreed with the diagnosis of sensory polyneuropathies. I have been thoroughly tested for the cause, and have been labeled “idiopathic.” One neuro told that because my arm EMG was normal, it showed there was no cervical nerve root involvement. I have a few questions regarding the EMG/NCS. First, why would the neuro not perform the ordered EMG on my leg? I have a sneaking suspicion that my lower leg paresthesia could be due to lumbar nerve root involvement, which I assume the EMG would have shown. He simply did the NCS. Also, can an impinged spinal nerves cause demyelination? I can’t seem to get an answer from the docs. Would they be able to differentiate between idiopathic PN and lumbar problems on the NCS? I just want to know for sure if my lower back is causing the lower extremity problems, and the EMG/NCS is Greek to me!

Answer

In cases like yours, these findings would indeed indicate to me the presence of a peripheral neuropathy. Peripheral neuropathies can be due to a host of things, first and foremost diabetes (or a family history of diabetes), alcohol consumption, toxic or occupational exposure to heavy metals or solvents, thyroid disease, gout, multiple myelomas, dysproteinemias, immune deficiencies etc. only to name a few. Leg paresthesia could indeed be due to a lumbar nerve involvement which could only be detected by the needle exam, but given the whole picture, of course it could also simply part of the neuropathy. An impinged spinal nerve can cause demyelination, which is difficult to detect from the routine nerve conduction studies. And finally, it is very difficult, by NCS alone, to distinguish between a lumbar problems and peripheral neuropathy. I hope this helps.

Time lag before fasciculation

Is there any time lag between when nerve damage occurs and fasciculations make their appearance i.e. can they appear almost immediately after the damage, unlike the fibs and sharp waves which don’t appear for two months? Thanks a lot again.

Answer 1

Fasciculations are very different animals than fibs and positive waves and are usually seen in diseases such as ALS (Lou Gehrig’s disease) and not following simple nerve damage

Answer 2

I am not sure what do you refer to by “nerve damage”. However, fasciculation is not a feature of traumatic nerve lesions. It occurs in anterior horn disease, radiculopathy, and demyelinating neuropathy. I must say that I do not encounter any time lag between the onset of illness and development of fasciculation. Unlike the fib and positive sharp waves. Also, the finding of fasciculation alone is not pathological. Another point that complete relaxation is needed to recognize reliably the fasciculation. Furthermore, there should be ample time or pause between the needle movements

“Benign fibrillations”

Can a fibrillation be also benign (without serious pathological meaning)? I have read somewhere that a person was having an EMG in MAYO clinic and the doctor found one fibrillation in his thigh and told him that the test does not suggest ALS or other form of denervation. I have also read that people who exercise a lot have sometimes fibrillations in EMG. So, can a fibrillation be totally benign?

Answer

Yes, fibrillation may have no or unexplained clinical significance. In a way it could be considered as benign, why? Perhaps because they are present in certain muscles in good number of asymptomatic subjects. Let me give you some numbers; in foot muscles, fibs and PSW reported in 6-29% of “normal” subjects. In lumbar paraspinal muscles, fibs and PSW seen in 15% of “normal” subjects and in about 30% of an older group above 40 years of age. Because those subjects are asymptomatic, isolated fibs and PSW in those muscles are not necessarily indicative of neurogenic process. The presence of fibs in other muscles, therefore, is significant. However, isolated fibs in the thigh (as in your case) do not mean ALS because it did not fulfill the other criteria of EMG findings in ALS, it could be radiculopathy. The fibs and PSW to be clinically significant, they should meet 2 criteria. They should be recorded away from end plate. Secondly, they should be recorded in at least 2 muscle sites. The important point is to keep in mind that their presence should always be interpreted in the clinical context, as EMG is only an extension of clinical medical/neurological examination. Thanks.

Comment

WELL, THANKS for the thorough answer. So if there is a disorder of benign fasciculations where a bunch of muscle fibers fire spontaneously, maybe there is a condition where singular fibers fire spontaneously! My question is: Have you ever seen patients with benign fasciculations AND such harmless fibrillation?

Answer

In brief, no, I did not recall a “normal” subject with combination of fasciculation and fibrillation in the same muscle. They do indicate pathology, but maybe insignificant if no other muscles are involved and the patient is asymptomatic, for instance, isolated changes seen in foot muscle (ext. dig. brevis), however, a follow up is recommended. I think practically, it is appropriate or safe to say that finding a fibrillation is abnormal unless proved otherwise (not the same rule for fasciculation). Of course, fibrillations are harmless but an important clue to diagnosis within clinical context.

Accuracy of an EMG test in muscle weakness and tenderness

I have Chronic muscle tenderness along with weakness for four and a half years, a recent EMG was normal and suggested no myopathy was responsible. I am concerned that such persistent muscle pain is not due to some disease activity – could the EMG test have missed something, because only my left upper arm and my leg muscles were tested. Thank you

Answer

What you describe sounds like fibromyalgia which causes muscle aches, generalized fatigue and sleep difficulties. An EMG is generally negative in Fibromyalgia. Physicians who specialize in Physical Medicine and Rehabilitation (also called Physiatrists) usually are more familiar with this condition and its treatment. Best of luck.

Normal EMG recording from the muscle at rest

Does increased insertional activity look exactly like fibrillation and positive waves or it may have totally another form? From what I read both have the same form but increased insertional activity never becomes spontaneous/ when you say a normal resting muscle is electrically silent, does it have to be “completely straight line” like a “dead heart” Because on my EMG there was not straight line (in some of the muscles) but like regular “wavy line” – I know these were not positive waves because they were upward (negative) and not downward and I think It was not a fibrillation either because these waves were wide (according to the books the fibrillation wave is vary narrow – very short duration) . Could this be increased insertional activity? *The doctor said It was nothing serious just “something from the background” and that the muscle is not totally relaxed and that is why he could not reach the “straight dead line” – what did he mean, could this be increased insertional activity? There was “full interference pattern” in these muscles and normal motor units. THANKS IN ADVANCE

Answer

It is like that, at rest nothing is seen, no “spontaneous” activity in normal muscle. It should be as you said completely straight line (as you said dead heart, it is interesting term, although this term is not used in our field and may not be preferable or we did not think about it). However, this line may not be straight because the patient is not relaxed or something from background (not pathology). In your case seems like an electric interference (60 Hz) which has no significance. It is not prolonged insertional activity from your description

Comment

THANK you! Can you relate more specifically to the descriptions? 1. Is that true that fibs look like brief spikes and not like wide waves? 2 Is that true the increased insertional activity has the shape of fibs and positive waves? And if not what other shape it might have? 3 and finally, Does the electric interference you mentioned as a possibility has something to do with the muscle being tense and poorly relaxed or it has nothing to do with one’s muscle condition during insertion I would appreciate deeply your answer! THANK YOU!

Answer

Back again, sorry for being rather late. Answer 1: Yes, fibs are spikes but with characteristic features. Answer 2: No, insertional activity does not look like fibs or PSW. For 1 and 2, the site contains good description for both. You may use the search engine. Answer 3: This interference (artifact) has nothing to do with your muscle or yourself.

Effect of Tegratol on EMG

I am going to have an EMG later this week. I am taking the following meds: Tegratol XR 100 mg twice daily. Alegra – twice daily, not sure of the dosage. Will either of these make a difference in my EMG? Thanks for any information!

Answer

No, none should affect your EMG results.

Electric stimulation and its relation to CMAP amplitude

I think this question is a tough because I cannot find the answer in any book does the CMAP (compound muscle action potential) Depend on how powerful the stimulation is? I am asking that because I had 2 EMG’s and although conduction velocities remain quite similar the CMAP are very different – in one of test I was given very powerful stimulation (there the CMAP was much higher) – in the other a very weak stimulation-lower CMAP. for example, for left peroneus it changed from 3.4(first EMG) to 13.28 (second EMG) (the higher were where the stimulation was higher) if it is not the power of stimulation – what else could make such a difference ? Thanks for taking the time for reading this!

Answer 1

You are right, the CMAP depends on the intensity of stimulation, i.e. the stronger the stimulation the higher the CMAP (up to limits). Also, another factor is the way of stimulation for instance how close the stimulator electrode or probe to the nerve

Answer 2

Stimulation needs to be about 25% above maximum, not more than that, otherwise you will be stimulating other nearby nerves and getting volume conduction from them which would account for the higher amplitude.

Comment

thank you for responding me! You said the higher the amount of electric current – the higher the CMAP is! As I said in my case there was great difference (3mv versus 11mv) – so How the normal CMAP for the ulnar nerves, for example is defined? When the books say the normal CMAP is XXX, Do they relate to the one they get in MAXIMAL or MINIMAL stimulation? (there is great difference!)

Answer

As discussed in the last few emails. The CMAP is measured by adding about 25 % of stimulus intensity after obtaining the maximum response. We do not take the response after minimal stimulation.

Description of EMG Exam

I am scheduled to have an EMG Test on my calves because of pain while walking. I looked through here and could not find a description of the actual test. Could someone please give me an idea of what to expect, how long it takes and then what the test will reveal when it’s over. Thank you.

Answer

This EMG test consists of probe inserted in the muscle and this test is associated with little discomfort or pain (quite variable between subjects). The examiner may also apply electrical stimulation to study your nerves, this kind of electrical stimulation is mild and tolerable even in children. Some children having fun with it. However, EMG would be helpful in your case to find out what is causing your pain and can exclude nerve compression from lower back in your case.

Patient response to nerve conduction test

Today I had a NCV performed and when the doctor tested my Ulnar Nerve (Right Armpit) my right leg jumped! This happened each time he tested it? Any ideas? When testing my left arm my whole body jumped (flexed)? Are these normal or indicative of a particular problem?

Answer

Do not worry. This does not indicate problem. This seems like a reflex reaction as somebody is taken by surprise

EMG “Number of insertions”

I realize this is a bit of an overworked subject but I am a bit confused. In reading some of the previous posts here on the forum regarding needle EMG, you stated: “The needle EMG part of the test consists of inserting needle probes in the muscles, usually, 4-5 such insertions per extremity.” What I am confused about is that the online EMG manual you talk about studying 20-25 MU per muscle, calculating average amplitude, phasing etc. Since I assume by your post listed above you are referring to studying 4-5 muscles per extremity. Even with testing in multiple directions after insertion, is it possible to study 20-25 units with one insertion (stick) per muscle? Also is doing one needle insertion per muscle, again testing in multiple directions, enough to detect spontaneous activity in even mild involvement or early in a disease process? Thank you very much.

Answer

What I should have said is “usually, 4-5 such muscles (not insertions) per extremity”. In each muscle I usually do one insertion but sample the muscle in 4-5 different directions from that same insertion. Most of the time this is sufficient to detect denervation, but as you know, nothing is ever foolproof in this business, that’s why it is called an art, and an EMGer’s experience and familiarity with the various presentations of disease play a great role as well.

Comment

Thanks for the clarification. Do you normally test for minimal, moderate and maximal effort in each direction after insertion? Or do you just test for spontaneous activity in the 5 directions and only test (as seems to be very common) for voluntary in one. Finally do you test for both spontaneous and voluntary activity in the paraspinals? My doctor had a hard time finding a position (he had me on my side) where I could totally relaxed. He rocked me back and forth and got short moments of total relaxation and no activity. He said he could see there was no spontaneous activity in the half second or so long relaxed moments. Is this a valid test?

Answer

In routine everyday work, I check the activation (mild, moderate, full) in one or two insertion points only. When I am doing a quantitative study and locking for abnormalities, I look in more places. Paraspinals are indeed hard to relax and I usually check only the insertional activity in them. So you catch what you can get when they are difficult to relax and frequently that is sufficient.

Worried about having NCV study

I’m going in to have a nerve conduction test on Monday. I have extensive damage to my left hand due to a weight-training accident 2 years ago. My muscles have atrophied and I’ve been in constant pain since mid-January of this year. I’ve lost almost all use of my hand. I can barely type or write with it. I know I have to have this test done, but I’m worried because I hate needles. Is there anything I could be told to ease my fears? I already read the FAQ. But that made things worse.

Answer

Of course I cannot stop all your worries but allow me to tell that I had such test before, it is not that bad at all, you may feel little discomfort. It is a sort of probe to examine the muscles. I am sure you will find it much easier that what it looks like. It will help you not to hurt you. Think positively that way. I am certainly sure you would find the test very much tolerable as I know not only in myself but also for thousands of patients I have seen. All the best.

Comment

I had my test completed. What was I supposed to expect? My hand barely twitched on the shocks. My fingers twitched and my hand raised off the bed once. Thats it. My mother had one a few years ago and she said she almost smacked him as a reflex. On the sticks, they hurt like hell and I bled. 3 were silent and 2 made a lot of noise and he had me move my elbow or thumb. The pad by my thumb hurts really badly right now. After my test, my hand was paralyzed. When Id try to move my fingers Id get no response and eventually I got them to twitch a slight bit. . Theyre back to normal now. But hurt so badly. Im about o take some painkillers and go to bed. So, is this normal? or is it all a bad sign?

Answer

Yes, post EMG local pain or soreness (due to local tissue irritation) does not last long. Usually will disappear in the same day, rarely to next day. Your symptoms could be related to your primary illness. I think you should consult your neurologist to check your EMG results and accordingly management is offered.

Comment

The muscle by my thumb hurt really bad last night. Now it hurts and is more swollen. the muscle is atrophied.. But it’s swollen to twice the size of my other hand. I cant use my fingers. But thats probably just due to aggravation of the condition. I had to call in ‘sick’ to school because my left hand is the one w/the problems and Im left handed.

Answer

I share your feelings and pain. It seems that the pain is out of proportion. Although, I must say and should be very clear that it is difficult to decide from your symptoms, but it is perhaps a kind of/or part of it related to sympathetic nervous system dysfunction. Again, further consultation with neurologist is worthwhile.

Effect of hand Squeezing on LL NCV

When Having my conduction velocities study, It seemed that the neuro could not get what he wanted when giving me the electric stimulation to my legs (peroneal, tibial nerves), he then told me to squeeze tightly my hand and only then did he got what he wanted to get and said all was fine. Dear doctors! What do you think he could not get (I think I recall he said It was the Amplitude)? Was it “legal” – I mean I am just curious whether getting “the wanted NCV result” that way is all right and not “cheating”? THANK YOU FOR READING THIS AND RESPONDING!

Answer 1

That’s is usually to get the F-wave (https://www.teleemg.com/jbr070.htm) in the lower extremity, and it is a “legal” maneuver.

Answer 2

Squeezing the hand during EMG helps to get better amplitude fro the evoked response: F-wave, H-reflex or a motor evoked response. Squeezing the hand is also asked to at times, by physicians during a clinical examination to obtain better deep tendon reflexes.

Hand contraction with EMG of LL

In read in previous post that it is quite common to ask the patient squeeze his hand in an EMG. A month ago I had my EMG and the neuro said he was not getting good CAMP amplitude as He had wished to, so told me to squeeze my hand. He also “hit” me with tremendous currents, and then he got normal CMAP. (Also read posts in this forum about it) About the nature of CMAP amplitude – A. How far can it change with higher currents, can it get from 2 to 15 MV (in supramaximal stimulation+25%)? in MU – How much can it change in low and high currents? B. In which current does he have to stop? Is there a “limit current” in which more current would not produce higher amp or “the sky is the limit”? C. And about the “squeezing the hand” thing – IN MV- HOW higher can it get? I mean, how much additional MU can squeezing the hand yield? (2,5,10,15)? And MOST importantly for me why some people get the right CMAP amplitude without squeezing the hand while others should do so – Does it depend on the physical condition of one’s nerves or not – I mean if he asked me to do so – Is there a problem (even minor) with my nerves? Hope to get your insights on these “CMAP THINGS”

Answer

Thank you Rob. As pointed out in previous posts that squeezing increases the motor response, it works by enhancing the response. Of course it will work to certain limits. To answer your point, it may increase from 2 mV to 15 mV. Once the maximum level or value is reached, then any further increase of current will lead to stimulation of the nearby nerves giving a false result. Therefore, only a 25% increase of stimulus is added after obtaining the maximal CMAP response to avoid such stimulation of other nearby nerves. All commercial EMG machines have limit of stimulation, which cannot be exceeded for patient safety. This squeezing method does not reflect any pathology of the nerves but just a physiological variation between individuals.

Comment

What Do you mean by maximal response? How can the examiner know when is the maximal response for a certain nerve? Because as you said, the higher current you give the higher amplitude you get! So how Does the examiner know when he had reached the point where he gets false increase from nearby nerves? How does he know what is the real “maximal CMAP response for a nerve?? (And that from now on he crosses the limit of stimulating neraby nerves) * What would be the range of normal CMAP for the peroneal? , Tibial? And ulnar?

Answer

The following should help to get the best response. First of all the examiner should be familiar with the anatomy of the peripheral nerves. A surface electrode is used for stimulation; it is easier and less uncomfortable for the patient. The cathode of the stimulating electrode should be placed over the nerve closet to the recording electrode. The anode is placed parallel to the nerve, away from recording electrode, you may rotate it to minimize stimulus artifact. The nerve should be stimulated with stepwise increasing strengths. Enough current must be applied to activate all of the axons of the nerve. This amount, called supramaximal response can be obtained with an electrical stimulation of 10-75 mA and pulse duration of 0.1-0.5 ms. Over stimulation would produce latency artifactually short or a conduction velocity too fast for that nerve. Also, stimulation of adjacent nerves could produce CMAP larger than expected and has initial positive deflection (except tibial nerve). That how I would make sure it is a response from that particular nerve and no contribution from other nerves. This problem is encountered commonly between unlar and median nerves at thr wrist. Normal values from Liverson and Ma 1992: ulnar CMAP between 4-22 mV. Tibial CMAP 5.8-32 mV. Peroneal CMAP 2.6-20 mV.

How does medication affect EMG test?

I’ve been taking Toprol, Wellbutrin and Lipator for about three years..I recently took an EMG and I wasn’t asked about any of the medication I was taking..how would this affect the results of the EMG?

Answer

None of these medications would affect your EMG results

Meaning of increased muscle irritability

I would appreciate your relation to the following point: The issue of the so-called irritability is mentioned in the EMG manual and also in the forum. Yet some of the features are not clear: 1. Prolonged insertional activity=irritability??? 2.does irritability look like the spikes of fibs and PSW – does it look like spikes at all? Does it have a typical sound – what is it like and how long does it persist? 3.The relation to denervation – in the manual It is said that irritably is seen in early denervation – How early Do you see it in denervation? I know that for fibrillations it takes 2 months – Is it the same for irritability or does it appear earlier?

Answer

Thank you for these basic but actually interesting questions; my comment will be divided into 2 parts, first quick As to your Qs and second is a general description. First: 1. Yes, increased insertional activity (IA) does indicate irritability. 2. IA looks as spikes but they are not fibs or PSW, sound like perhaps “crack”!!. 3. Increased IA occurs before fibs and PSWs. Second: The IA is considered as “injury” potentials due to needle movements in the muscle, this is causing irritation of the cell membrane. They come in bursts each usually lasts 75-400 msec. following each needle movement, each burst formed of several muscle fibers (normal phenomenon). Hyperexcitability of the muscle membrane leads to prolonged IA, for instance, in early denervation before appearance of fibs and PSW. Practically I find the increased IA develops several days before fibs and PSWs, I think related to the affected nerve length. Regarding the appearance of fibs and PSWs, it is axon length dependent (not 2 months). The shorter the distal part to the lesion or stump the faster the fibs to appear. Some practical lesions; about 7-10 days seen in paraspinal muscles after disc lesions, but about 4 weeks in distal muscles. Longer in the lower limb muscles compared to upper limb muscles. After facial nerve lesion, fibs could be seen by 8 days. Also, practically, I usually suggest an early lesion or nerve “irritation” with prolonged IA, but do not make (or attempt) conclusive evidence out of it. A follow up is usually needed if those patients are seen that early. I hope this will answer all your questions. Thank you

Comment

HI! Thank you so much for your answer about irritability! My question refers mainly to ALS (mnd): – I did not read irritability in connection to ALS (but fibs and PSW) so my question to you is: according to your experience how common irritability is with ALS -Did The majority of your ALS patients come with irritability or fibs and PSW???? (From what I understand irritability is seen mainly with “simple” nerve injury not als?? and due to the rapid progression of ALS fibs and PSW are always seen the first EMG- you never “catch” an ALS patient that early to see irritability??? Thank you again!

Answer

Right, this is important point, in patients with ALS; I have never considered increased insertional activity as evidence for muscle involvement, but look for the definite denervation activity. I believe that increased insertional activity has no practical significance in ALS.

Comment

Thank you for the previous reply. So according to your experience, Do you find irritability (in ALS) prior to denervation in the ALS patient’s FIRST EMG (such as in simple nerve injury) and if so what is the time for fibs to appear in that case? or by the time there is irritability there are always signs of active denervation as well (fibs,PSW) in ALS – never irritability alone.. in ALS even if very early.

Answer

I do not know the answer to your points. Practically, I look just for signs of denervation in ALS and do not actually considered looking into increased insertional activity per se.

Comment

The diagnosis of amyotrophic lateral sclerosis (ALS) being so dramatic for the patient, we need to have strong evidence of peripheral neurogenic involvement we are looking for signs of denervation such as fibrillations, positive sharp waves not only insertional activity. Fasciculations and reduced recruitment pattern of large motor units are also important EMG sings in ALS?

Answer

Absolutely correct, I agree with you. Stringent criteria always needed to be fulfilled.

Identical sounds of motor units in unrelaxed muscle vs. fasciculations.

Dear Doctors! I know that motor unit firing at rest in an EMG test (due to poorly relaxed muscles) is quite common. However they produce popping sounds (“like pop corn machine”), which is the same sound (popping) of fasciculation potentials so how do you distinguish fasciculations from firing of normal healthy motor units (of poorly relaxed muscle)? As they both produce the same popping (popcorn machine like) sound? (By their rhythm, regularity or something else)?

Answer

Practically speaking the patient should always be relaxed, otherwise I cannot tell whether the potential is fasciculation or voluntary firing MUP.

What can EMG tell? Relation of tingling to level of B12

Have had these symptoms for following month. FATIGUE, kinda dizzy/lightheaded like in a fog, or had 1 alcoholic drink, legs, mostly left shaky like jello inside and weak, Cold feet, twitching, and slight numbness along anterior aspect of left shin. Doc referred me to Neuro who is doing an EMG. What will this tell me? Also, I insisted on a B12 level (which he thought I was reading too much about) and the level was 148 pmol/L. The range said anything >150, NOT deficient. 110-150, POSSIBLY deficient, and <110 PROBABLE deficiency. Could this, even though only slightly under the “normal” range, be the root of my problem???

Answer

Yes, peripheral neuropathy is quite possible from your symptoms; therefore EMG should be useful to decide about neuropathy. Of course the history and clinical examination of your neurologist is equally important. The examination should help to suspect if you have B12 deficiency as a cause. He should decide if you need other investigations if needed. However, the B12 level seems to be within normal limits.

Explanation for NCV report

Dear doctor! I hope you will be able to help me understand my NCV results. It is said. MOTOR NERVES: dAMP is. (For each nerve) and later AMP% is. For each nerve which is the actual amplitude of the nerves: AMP% or dAMP – what is the meaning I wonder because for the sensory nerves it is just AMP. *the dAMP are positive . AMP% – some are positive and some are negative. (-10,-20,5,-17) For example left ulnaris (motor) dAMP is 7 while AMP% is 5.

Answer

The dAMP stands for motor response at distal site. Another stimulation at proximal site will produce a response. This proximal response is either higher, similar or lower (-) amplitude expressing as AMP% compared to distal response (dAMP). While the sensory response is only done at one site, so no comparison with proximal response.

Response of latency and amplitude of CMAP to increasing stimulus intensity

Dear doctors! In previous posts the issue of the connection between the amount of electricity and the CMAP was discussed. However, one thing remains unclear: We know that the more current you give, the higher the CMAP is and (also the latency get shorter and we get better conduction velocity) However which of these two factors is FIRST influenced by the amount of current? As far as I know the latency and conduction velocities reach their “best scores” before the CMAP, I mean by the time you reached the optimal results for velocity and latency, you have not reached yet the maximal CMAP amplitude and there for more current is needed? In other words, in order to reach optimal results of velocity and latency, less current is needed than for the maximal CMAP amplitude CORRECT? Looking for your insight on that matter

Answer

I disagree with that concept for the following reason; when you use a submaximal stimulation it might happen that the most rapidly conducting fibers were not stimulated so the latency is too long (those fibers are responsible for shortest latencies and fastest conduction velocities), therefore, it is custom to increase the stimulus intensity until you get highest CMAP. Then we know practically, that the fastest conducting nerve fibers are stimulated and latency is the shortest and CV is the fastest.

Is it neuropathy or not?

In letters to my G.P. my neurologist has noted that I have “decreased pin sensation, temperature distally in the lower extremities. Position sense and vibration sense are normal. Deep tendon reflexes are absent in the lower extremities and +1 in the upper extremities..Babinski’s sign is absent.” He recommended EMG/NCS. After testing, he reported “. Normal sensory nerve conduction in the left superficial peroneal nerve with distal latency of 3.68mS..motor nerve conduction in the right peroneal nerve is within normal limits with a velocity of 40 meters per second and distal latency of 6.40 mS and left peroneal nerve with a velocity of 44 meters per second and distal latency of 5.20 mS. The H-reflex in the right and left tibial nerves is abnormal in that there are no responses. He concluded “. Not enough findings to really indicate definite neuropathy since the sensory and motor nerve conduction are normal.” Entering the left superficial peroneal nerve distal latency of 3.68mS and the appropriate age, sex, and height (41, M, 190cm) into the appropriate boxes on your lower extremity sensory/H-Ref teleEMG calculator (thank you very much) produced an MRV of -4.2. I wasn’t sure how to use the lower extremity motor calculator, but it may have produced negative MRVs of -1.1 or closer to zero. Three questions: 1) Neuropathy or not? , and 2) Can you recommend an unrelated source for normal values of EMG/NCS (I’m looking for corroboration) including books, and 3) recommend additional means of investigation and/or wait for progression. Based solely on reported findings (no foot problems, though arches somewhat high, thanks for asking), and slow progression over perhaps eight years or longer (just detected this, though deep tendon reflexes gone for at least six years), I am inclined to suspect some sort of very mild hereditary sensory neuropathy? Please reply. Thank You.

Answer

Looking at your history and NCS data; you have some symptoms and signs to suggest neuropathy, and some data in NCS to support that (absent H reflex, right peroneal latency of 6.4 ms and CV of 40 m/s). Absent H reflex is definite abnormality (neuropathy is one cause but not the only one), and peroneal nerve, to me, it is slightly slow but it varies according to laboratory normal limits, but anyhow, not enough by itself to say peripheral neuropathy even if abnormal. However, additional information would be useful and important for instance, sural nerve, amplitudes of motor and sensory responses, F wave and needle EMG examination and perhaps additional test for small fibers (sympathetic skin response). Looking at the duration of symptoms seems to be very slowly progressive if any. I think a follow up study is worthwhile after several months. About the last point being hereditary or not, I would say, this study cannot tell you that, you need more information in the history and further genetic study that could be discussed with your neurologist. I hope this is helpful.

Comment

Isn’t a conduction velocity of 40 completely normal for the preoneal nerve? If not what are the limits for this nerve in your laboratory?

Answer

MCV for peroneal nerve is 41 m/s or faster.

Why CMAP amplitude changes with change in stimulation current?

Dear Doctor! Is it true that according to the laws of electrophysiology the amplitude of the activated motor potential (CMAP) SHOULD NOT change theoretically with current changes? And if so how come clinically there is so many differences in CMAP due the amount of current? (In my test It went from 4(lower current was given) to 15 (higher current was given)-in 2 different tests? THANKS IN ADVANCE?

Answer

This is important point, but a little complicated. I will try to explain it. The CMAP (also called M wave) is compound muscle action potential therefore it represents action potential recorded from muscle when a motor nerve is stimulated activating some or all muscle fibers in that muscle. The nerve composed of axons, when each axon is stimulated by electrical current at threshold, following the role of all or none (all or nothing), the muscle fibers innervated by that stimulated motor axon will generate activity or share in the formation of CMAP. But not all axons are stimulated or reaching threshold at the same stimulus intensity, as they are (relatively) at variable distances from the stimulus electrode. That is why we use supramaximal stimulation with proper stimulus position to make sure that all axons in the nerve are stimulated, so maximum CMAP is obtained.

What is Interference Pattern in EMG recording? Muscle contraction & spontaneous discharges

What does 60%FF Effort Mean? On EMG reports, there is a column for Interference Patterns with the following Options: %Full Pattern Discrete Single Recruit. Ratio Effort I have read your manual, but have not found anything that gives those kinds of values. Is this the decreased rate of recruitment? What does this “Effort” mean and what are the normal values for it? My other question is, I see that things like mild effort, etc. is mentioned. Should the examiner be asking a person to contract muscles while they are doing the EMG?

Answer

The interference pattern is part of the EMG study to see in simple terms how much the patient can contract his muscle. The examiner or electromyographer will ask the patient to contract the muscle in 2 steps first mild contraction to study the motor unit potentials and then maximum contraction for the interference pattern. 60 % effort, for instance, would mean generally that the patient did not produce full contraction. However, this does not mean always a pathology”.

Comment

My next question would be, why would I not be asked to contract my muscles? Is it or is it not normal procedure to have the person contract muscles? If I had been asked to contract muscles, would this have given a better response? This FF percentage ranges from 30 to 70 % (1 muscle). I had leg and arm tested. The gastrocnemius was on 30%, biceps 40%, Abductor digiti 40%, rt. extensor 50% interrupted, anterior tibialis 50%, vastus medialis 60% and abductor pollicis brevis 70%. I was not asked to contract any muscles. What pathological conditions cause this? Is ALS one of the conditions? (My aunt died from ALS so this is always in the back of my mind) Can plates and screws in my neck cause it? Can these plates and screws be causing a severe spinal stenosis of some type? Can it be some kind of demyelinating disorder? My report said that there is no neuropathy, no radiculopathy and NO something else. According to the report, there was nothing wrong, yet I walk with an abduction and am quite weak and spastic. In fact, they operated on a Thoracic Disc thinking it could be contributing to the problem, wrong. Surgery didn’t help and left a few more secondary problems. I have lots of bulges, and spondylosis. I am quite myelopathic. I had bi-lateral positive Babinski, clonus etc. Recently my toes did nothing, no up no down. Nothing. I am assuming that this is now indicative of lower motor neuron damage. I really would like to know what could be done, if anything. I would also like to know if those kinds of readings could indicate ALS as I would then go to the appropriate MDA Clinic for testing instead of beating my head against the wall trying to surgically correct the uncorrectable. If it is radiculopathies, why don’t they show up? The doctor said, central nervous stuff doesn’t show up, so now I am quite confused. If it is radiculopathies, they don’t show, if it is central it doesn’t show so what was the purpose of the EMG’s. What pathological conditions cause that kind of patterns?

Comment 2

One other question. Does contraction of the muscles have any bearing on whether or not one would see any spontaneous activity such as fibrillations, positive sharp waves, fasciculations, myotonia or repetitive discharges?

Answer

First asking the patient to contract the muscle during EMG is a normal procedure, if the patient can contract voluntarily. Otherwise, if the patient cannot contract his muscle for any reason, I just examine or do EMG to see if there are any spontaneous discharges. Contracting the muscle has nothing to do with production of Fib, PSW, etc. On the contrary, we ask the patient to relax his muscles, because such spontaneous discharges are seen at rest. Contracting the muscle would simply obscure such discharges.

Relation of interference pattern with upper or lower motor neuron diseases

Concerning spinal stenosis. Could severe spinal stenosis cause reduced interference pattern, or is it just upper motor neuron diseases?

Answer

The reduction in the interference pattern (IP) is not specific for any particular lesion. A lower motor neuron disorder could be a cause, as in your case severe spinal stenosis. As I said in previous post that reduced IP may be variable and changes with the patient’s cooperation, the strength of the muscle, pain and the presence or absence of disease of upper motor neuron such as spasticity. A combination of factors is quite possible as cause for IP in your case. However, we cannot take it as a solid parameter by itself, but always other EMG parameters are required to support it. Final word, I must say that IP is not specific but it has diagnostic value by doing quantitative analysis of IP (and concept of cloud) in lower motor neurone diseases