Transcarpal motor conduction velocity in carpal tunnel syndrome.

Transcarpal motor conduction to abductor pollicis brevis (APB) was evaluated in 43 patients (70 hands) with suspected carpal tunnel syndrome (CTS). Transcarpal motor conduction was abnormal in 80% of hands compared with 11.5% with prolongated distal motor latency from wrist stimulation. Transcarpal motor conduction was comparable in sensitivity with transcarpal sensory conduction and 2nd lumbrical-interosseous latency difference. Transcarpal motor conduction is a sensitive test for diagnosis of CTS. Sensory fibers were no more susceptible than motor fibers to compression in the carpal tunnel, and fibers to APB were as susceptible as those to the 2nd lumbrical muscle.