Musculocutaneous nerve lesions

Causes

• Lesions of lateral cord of brachial plexus.
• Weight lifting or strenuous exercise may result in strech or entrapment injury of the nerve as it penetrates coracobrachialis muscle.
• Compression injury during sleep or anesthesia.
• Compression/entrapment injury by carrying heavy object on the shoulder with the arm around object (“carpet carrier’s palsy”).
• Distal injuries in the forearm may result from venipuncture or compression.

Symptoms & signs

• Proximal lesions result in sensorimotor deficits.
• Biceps and brachialis muscle weakness, atrophy.
• Isolated biceps weakness may result from distal motor injury.
• Isolated sensory deficit may result from distal injury in the forearm.
• Pain and paresthesias in the proximal forearm are aggravated by elbow extension.

Examination

• Test brachioradialis and biceps for hyporeflexia, inspect for atrophy and fasciculations, palpate.
• Assess forearm flexion strength: Ask patient to bend their elbow against resistance. Make sure the patient does not tense wrist flexors. To focus more on brachioradialis, assess with forearm midway in pronation.