Which nerve is affected in carpal tunnel syndrome?

• A. Ulnar nerve
• B. Median nerve
• C. Radial nerve
• D. Axillary nerve

Answer: (B)

Compression of the median nerve as it travels through the carpal tunnel is what defines carpal tunnel syndrome. This nerve provides sensation to the palmar surface of the thumb, index, middle, and the radial half of the ring finger, and it supplies the thenar muscles that control thumb opposition. When the nerve is pressed in the carpal tunnel, you get numbness, tingling, and often weakness in the thenar muscles, which fits the classic pattern of median nerve involvement. The ulnar nerve would produce numbness in the little finger and the medial half of the ring finger with different motor effects; the radial nerve affects the dorsal hand and wrist extension rather than the typical carpal tunnel sensory pattern; and the axillary nerve involves the shoulder, not the hand. So the nerve affected in carpal tunnel syndrome is the median nerve.