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Myasthenia Gravis

Q & A: Myasthenia gravis is a chronic autoimmune neuromuscular disease that causes weakness in the skeletal muscles, which are responsible for breathing and moving parts of the body, including the arms and legs.

LL burning and weakness “p. neuropathy vs. myasthenia”

If a patient presented with leg burning, bilateral, and leg weakness, would not an EMG/nerve conduction study be one of the first tests a doctor might do? These were my symptons, and after two years, five neurologists, not one doctor did an EMG, until ten days ago. Diagnosis. Peripheral Neuropathy and possible Myathenia Gravis. From what I have read, it appears if the legs are burning, pain caused just by the touch of a hand, a sheet, or clothing, that an EMG should have been one of the first tests completed. What is your expert opinion? Thank you.


Your symptoms are a definite indication for EMGs. The burning feet are due to what we call a small fiber neuropathy, usually seen in patients with Diabetes or nutritional disorders. Symptoms of Myasthenia include fatiguability, double vision, droopy eyelids etc. It is important to find out how sure is the Doctor who did the study on you of the Myasthenia diagnosis, or if he/she needs to refer you to a specialist in this disease, because if you have it, you need to be treated.

EMG assessment for Myasthenia Gravis

I was diagnosed with myasthenia gravis in l995 with the positive aChR. antibody test and positive tensilon test. My neuro. is sending me to another neuro. at a MG Clinic at their medical school where they notified me that they will do a EMG/NCV w/Rep Stim testing after my office visit with the new neurologist. My question is: If my EMG should be negative, will I be diagnosed as NOT having MG? I am presently on social security disability and would not want to risk losing that. I have been notified to stop the mestinon the day before the test. I also take prednisone, Paxil and Klonopin but they did not ask about any other medication I was taking. I would appreciate any information. Thanks

Answer 1:

A positive antibody test is a very specific indication that it is Myasthenia. Repetitive stimulation needs to be performed in an involved muscle in order for it to be positive (it is important that you do not take the Mestinon prior to the test). A more sensitive test for Myasthenia is called Single Fiber EMG which has a higher diagnostic yield than repetitive stimulation. Good Luck.

Answer 2:

You are already diagnosed as MG. Therefore, it seems that the reason behind repetitive nerve stimulation test to check the degree of weakness or probably trying to reduce your medication. He advised you to stop mestinon before the test because it affects the result. A normal repetitive nerve stimulation test (decrement test) does not mean that you do not have MG. We know the test can be normal in MG. Just go ahead and all the best.

Question about MCD and MSD?

Thanks so much still wondering if you can tell me about these results. Single Fiber EMG: Extn.Dig.Com Rt Number of Recordings analyzed: 25 and Number of Recordings with blocking: 16% Mean Test Values are: MCD 55 / MSD: 56 / Percentage of recordings with blocking 64% I searched Medline but the information about Electromyography studies does not give normals either for the MCD or MSD I was hoping you could answer what these results mean. I was told that 16 out of my 25 nerves tested had 80% blockages how does this differ from the Percentage of recordings with blocking stated as 64%? A few people on the list will mention that they were told their EMG’s showed 50% but they haven’t understood that either in regards to SF EMG testing. Is that the MCD and MSD? Are my results as MCD 55 and MSD 56 percentages based on something? If so what? Thank you so much for your help and for answering all of my other questions? Kind Regards,


The neuromuscular junction is concerned with impulse transmission from the nerve to muscle. Normally, it takes time, this time is calculated very precisely for each muscle in normal persons. Normally there is little variation in this transmission. It is termed jitter i.e. there is normally a jitter up to a limit, once exceeded it is considered as abnormal for that muscle. This is calculated in mathematical way using the Mean value of Consecutive Differences MCD and Mean Sorted-data Difference MSD (Standard Deviation SD was not used because it would give erroneous results). All these done nowadays by computer analysis in the EMG machine. Practically the MCD value is used (only in certain situation MCD/MSD index and MSD are used). The normal value for MCD (jitter) for EDC muscle is 40 us (for the method used in your case, axonal stimulation). So value of MCD is compared to normal value obtained from normal persons for same age. I hope this will answer all your queries. Please write again for further question or unclear point.


Am I to understand then that the MCD and MSD are for jitter results and the other result is for the blocking percentage on all 25 nerves tested even though only 16 of my nerves showed blockages?

I know these are the two things they are concerned with, from what I read, in testing for Myasthenia Gravis. When a neurophysiatrist states then that an EMG showed a percentage of something then they are talking about the overall percentage of blockage in the total of nerves tested? Is this correct? I was told that 16 of my nerves had 80% blockages even though the final percentage stated is 64%.

Another way of asking since I don’t understand the terminology for electromyography tests is: Is this percentage then based only the total of nerves tested against those that were found to have blockages? In other words this overall percentage is more important than knowing the total of blockage percentage of each individual blocked nerve.

You mentioned that the MCD and MSD are not usually tested. Is this because Myasthenia Gravis is one of the diseases that effects jitter and needs to be obtained for a MG diagnosis?

Does the higher rate of MCD 55 and MSD 56 which shows jitter above the normal for the EDC nerve of 40 mean that it is faster or slower. Is jitter faster in Myasthenia Gravis or slower? I understand about the nerve synapse and how the receptor ends are blocked by antibodies which does not allow the normal impulse from Acetycholine transmission. So the blocking that is being tested for makes sense to me. It would seem to me that jitter would be slower also.

Thank you again for this great forum and the information you share. This helps so much to understand these tests and how they help to diagnosis our diseases so that we can get the help and treatments we need to get back some kind of quality to our lives.

I am working with AAEM right now as a patient advocate in Sacramento to fight a bill SB 1600 that was presented by physical therapist to allow them to do Needle EMG’s and diagnosis patients. We are opposing this bill as for all the reasons you state in your site that it takes a qualified physician in neurology to understand and diagnosis these tests properly. If I had been sent to someone who did not know about Myasthenia Gravis or how to even test for it (or what to look for) I would still be undiagnosed and untreated. This test was my only confirmation to my MG diagnosis.

I suffered for over 6 years without treatment, so weak, breathing and choking problems. Loss of my fitness level and had to close my health club from all my medical problems. It is very scary to think that PT’s who are unqualified to perform some of these very specialized tests are trying to also enter this field with only 8 weeks of training. It would be devastating and tragic to see so many people with neuromuscular diseases go undiagnosed, misdiagnosed and possible die from not having some one who is skilled perform their Needle EMG tests.

Thanks again for this great site and for sharing your special training and talent in EMG testing.


All your points are correct and your interpretation and analysis are correct. However, only one point about MCD, it is not only usually used to calculate jitter but the standard in Jitter measurement. Thank you again and you are welcome.

Attacks of fasciculations and nystagmus in MG patient on mestinon

I have muscle fasics every day. They are mild and completely painless. Most of them occur in specific areas of my body (left bicep, right thigh just above the knee, and right lower leg). What is happening when this sort of activity becomes amplified and fasics are occurring all over the body, from scalp to feet. Nystagmus is so bad that everything jumps/jiggles when I move my eyes, and with each step I take? This happened to me about a month ago and I wasn’t too concerned (thought rest would help) until I couldn’t empty my bladder at all. I wound up in the E.R. of a local hospital, and no one really had any clues, other than suspected Mestinon overdose (which proved not to be the case). I do have MG, but I don’t believe this “episode” was related in anyway to the MG. My husband could literally see my entire face “moving” spastically. This went on for roughly 2.5 to 3 hours. As mentioned above, I have fasics each day, but this seemed like a violent attack. Once the fasics eased off, I could finally void my bladder. I have been dx’d with spinal stenosis (entire spine) and have disc herniations (old injury). Any ideas on this would be appreciated.


Mestinon overdosage is known to cause fasiculation and urinary retention. But it seems you had an additional severe nystamgus, which is unusual feature. I would recommend seeing a neurologist with MRI of the brain. Also, he would check if the dose of Mestinon is appropriate or not.

Tensilon Swallowing Test in MG

I am going for a tensilon swallowing test. What kind of a test is that? I had a positive tensilon test and my abnormal lung test caused by mg and upper airway obstruction. I am sero-negative; I also have mild to moderate swallowing difficulties. I had a throat test where I had to swallow wires and showed low Les tone. Can you explain that? Thanks


As you said that Tensilon test in general is used in diagnosis of MG. To be specific, if patient complains of swallowing difficulty caused by MG, then a test injection of Tensilon should improve your swallowing. This is done by asking the patient to drink water before and after. This is the meaning of Tensilon swallowing test. Otherwise I am not aware of any other objective or quantitative explanation.

Myasthenia (Arm tested weak but EMG tested neg)

I am being watched to see if my myasthenia has returned, my eye is evident for ptosis, my right arm on testing the right one after a few seconds began drooping, my neurologist had extra time so we went in and did an EMG. The EMG was negative. Now my myasthenia is a mild case. And my neurologist and I are pleasant to each other, so he is not just a wall type doc to me, but this time he just said, well must be emotional, and no way to test the eye and left. So question. Is it correct, is it black and white, negative EMG, negative myasthenia (at least for the arm)


The answer to your question is yes/no: It is difficult to have black and white in medicine, although we wish to. Now, we have two kind of “EMG” tests used for Myasthenia Gravis (MG). The repetitive nerve stimulation (RNS) and Single fiber electromyography (SFEMG). If you had the RNS, then it is positive in about 55-77%, but I must say it correlates very well with the severity of MG. The other test the SFEMG is more sensitive 77-100%. If the test is done by experienced electromyographer and the arm is weak, then a negative SFEMG test in that weak arm means no MG.

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