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The radial nerve is susceptible to compressive neuropathy against the spiral grove of the humerus which can lead to neuropraxia.
When the upper arm is compressed against a chair back or bar edge sometimes from a lost battle with alcohol: Saturday night palsy.
When another individual sleeps on someone’s arm overnight compressing the radial nerve: Honeymoon palsy
From nerve compression from improper technique with crutches: Crutch palsy
If diagnosis not clear from history, DDx includes other entities that can also present with isolated wrist, thumb/finger drop
Horses: Radial verve palsy, CVA, C7 compression
- Most central disorders that cause arm weakness affect extensor muscles to a greater degree than the flexors.
Zebras: Lead toxicity, acute porphyrias (often polyneuropathy but upper extremity before lower and frequently distal extensors
Careful history and exam important in differentiating
In cases of peripheral compression against the spital groove the triceps maintains strength.
The distal extensors lose strength (wrist and fingers)
Including the thumb abduction (abductor pollicis longus is radial-innervated)
AND so will the brachioradialis
The brachioradialis (despite being a forearm flexor) has dual innervation from the radial nerve in 80% of people.
Brachioradialis strength is often preserved in a central lesion.
Best tested with arm supported on a surface in mid pronation/supination (hammer curl position) and have patient flex against resistance and evaluate muscle strength and bulk.