A 28-year-old carpenter develops progressive weakness of thumb opposition and thenar wasting. Nerve conduction studies show prolonged distal motor latency with preserved palmar cutaneous sensation. The compression most likely involves which specific anatomical location?

• A Median nerve at the pronator teres, proximal to the anterior interosseous nerve
• B Median nerve in the axilla, at the level of the brachial plexus
• C Median nerve within the carpal tunnel, distal to the palmar cutaneous branch origin ✓
• D Recurrent motor branch of median nerve after it exits the carpal tunnel

Explanation

The palmar cutaneous branch of the median nerve arises 5–6 cm proximal to the flexor retinaculum and does NOT pass through the carpal tunnel, which is why palmar sensation is preserved in carpal tunnel syndrome. The carpal tunnel contains the median nerve proper plus nine flexor tendons. Compression within the carpal tunnel causes thenar wasting and sensory loss over the lateral 3.5 digits, but not the palm. Pronator teres syndrome would affect all median nerve territory including the palmar cutaneous distribution.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.