Musculocutaneous neuropathy

Background

Musculocutaneous neuropathy is a rare peripheral nerve injury involving the musculocutaneous nerve, which arises from the lateral cord of the brachial plexus (C5–C7). It provides motor innervation to the biceps brachii, brachialis, and coracobrachialis muscles, and sensory innervation to the lateral forearm via its terminal branch—the lateral antebrachial cutaneous nerve. Injury to this nerve may result from direct trauma, shoulder dislocation, surgical complications, or repetitive overhead activity. Recognition in the ED is critical to guide appropriate workup, limit unnecessary imaging, and arrange early neurology or rehabilitation referral when needed.

Clinical Features

Motor deficits:

• Weakness of elbow flexion (biceps, brachialis)
• Weakness of forearm supination (biceps)

Sensory loss:

• Numbness or paresthesia over the lateral aspect of the forearm
• Atrophy of the biceps may be seen in delayed or chronic cases

Reflexes:

• Biceps reflex may be diminished or absent

Usually unilateral

Differential Diagnosis

• Cervical radiculopathy (C5–C6)
• Brachial plexopathy (upper trunk/lateral cord lesions)
• Median or radial nerve injury
• Axillary nerve injury (especially post-shoulder dislocation)
• Neuralgic amyotrophy (Parsonage-Turner syndrome)
• Humeral fracture with nerve involvement
• Supraclavicular trauma or compression
• Iatrogenic injury (e.g., from shoulder surgery or traction during anesthesia)