Which muscle group is typically weakened first in carpal tunnel syndrome?

• A. Interossei
• B. Hypothenar eminence
• C. Thenar eminence
• D. Wrist flexors

Answer: (C)

In carpal tunnel syndrome, the median nerve is compressed at the wrist, which primarily disrupts the motor fibers that supply the thenar muscles (the muscles at the base of the thumb responsible for opposition and abduction). When these thenar muscles weaken, you see early atrophy of the thenar eminence and a reduced ability to oppose the thumb, which is a hallmark finding. The interossei and hypothenar muscles are controlled by the ulnar nerve, so they tend to be spared early and don’t show weakness first. Forearm wrist flexors are also innervated in part by the median nerve, but CTS is a distal lesion, so their weakness isn’t the characteristic early sign.