Nerve:  Median

Compartments:  Thenar and central in the hand; and anterior in the forearm

Skeletal muscles:  All muscles in the anterior forearm except for the flexor carpi ulnaris and one-half the flexor digitorium profundus; flexor and abductor pollicis brevis, oponens pollicis, and lumbricals 1-2 in the hand

Cutaneous distribution:  Skin along the ventrolateral hand, palmar surfaces of digits 1-3, and the lateral one-half of digit 4. Deficits include the tips of digits 1-4.

Neuromuscular deficit:  Weakness when flexing the wrist and digits 1-3 and abducting the wrist and thumb under resistance. “Ape” hand resulting from impaired opposition of the thumb. Denervation is accompanied by thenar atrophy, extension of digits 1-3, adduction of an extended thumb, and cutaneous impairment along the distribution of the median nerve in the hand.

Differential diagnosis:  Lesions occurring below the mid-forearm (e.g., carpel tunnel syndrome) are limited to cutaneous deficits plus dysfunction the intrinsic muscles of the hand (see above). No motor impairment at the wrist.