What is involved?
Radial Nerve
Location
- Most frequently at the Spiral Groove of the humerus
- Could be at the Axilla (Saturday Night palsy)
- Or in the Forearm (Posterior Interosseous Syndrome)
Common symptoms
- Wrist drop, Patient unable to extend wrist or fingers up
- Almost always unilateral
- No associated pain
- Occasional forearm/hand/thumb numbness
- Symptoms always present no night/day preference
Onset
- Sudden
- Usually happens upon waking up one morning
- Or, after a “Saturday Night” at the bar falling asleep with arm hanging over back of chair
- Or following prolonged sitting in a position with arm leaning against sharp object
- Or following misplaced intramuscular injection in the vicinity of the Radial nerve
Risk factors
- No gender preference
- Diabetes or family history of Diabetes, Alcoholism
- Leaning on arms/axilla, sleeping in wrong position or with somebody leaning on arm, trauma
Exam
- When first seen, weakness but no atrophy – Wrist drop with inability to extend wrist, fingers
- Always check the three following muscles: Triceps, Brachio-Radialis, Extensor Indicis Proprius
- Triceps: Ask subject to extend elbow
- Brachio-Radialis: Ask subject, with thumb pointing to ceiling, to flex forearm. Make sure the belly of the Brachio-Radialis is easily visible (compare to healthy side)
- Extensor Indicis Proprius: With hand flat on bed, ask subject to raise index finger up
- Occasional numbness/decreased sensation over dorsum of hand/thumb area
- Difficulty spreading fingers (pseudo-ulnar interosseii weakness)
- Pseudo-Ulnar weakness correctible when wrist held level with forearm by examiner
- Positive Tinel sign (tingling upon tapping nerve) at the humeral Spiral Groove when lesion at that location
Localization
Three possible locations determined by exam of Triceps, Brachio-Radialis and Extensor Indicis Proprius.
- Axilla: Triceps, Brachio-Radialis and Extensor Indicis Proprius all weak, normal to decreased sensation over dorsum hand/thumb area
- Humeral Spiral Groove: Triceps strength is normal, weak Brachio-Radialis (can barely see belly of muscle) and weak Extensor Indicis Proprius, normal to decreased sensation over dorsum hand/thumb area
- Forearm (Posterior Interosseous Syndrome): Triceps and Brachio-Radialis normal, Extensor Indicis Proprius weak, normal sensation over dorsum hand/thumb area
EMG
- Very Good for localization (Axilla, Spiral Groove, Forearm)
- Very Good for Prognostic value: In pure myelin lesions (conduction block), recovery may occur after three weeks to a month
- In moderate/severe axonal lesions, recovery may take from 6 months to a year
- In mixed lesions, somewhere in between
Findings
- Slowing, drop in Extensor Indicis Proprius amplitude across compression area in myelin lesions
- Diffuse drop in Extensor Indicis Proprius amplitude with or without slowing in axonal lesions
- Mixture of above in mixed lesions
- Radial sensory spared only in forearm (posterior interosseous) lesions
Recommendations
- Symptomatic treatment
- Stop/decrease cause
- Wrist/finger splint to keep fingers extended in moderate to severe axonal lesions
- Passive wrist, fingers Range of Motion to maintain mobility
What else could it be?
- If other nerves involved, could be Brachial Plexus lesion (do not make the mistake of diagnosing a superimposed Ulnar neuropathy because the interosseii “appear” weak)
- Bilateral Radial palsies, always look for Lead poisoning
- Very rarely, Myotonic Dystrophy can cause weak, wasted forearms and bilateral wrist drop