WHAT IS INVOLVED

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Radial Nerve


LOCATION

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- 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

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- 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

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- 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

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- 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

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- When first seen, weakness but no atrophy

- Wrist drop with inability to extend wrist, fingers

- Always check the three following muscles:
.... - 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

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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

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- 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

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- 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?

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- 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