Carpal tunnel syndrome: use of palmar stimulation of sensory fibers.

In early or mild carpal tunnel syndrome (CTS), where the segment of median nerve sensory fibers is neurapraxic, stimulation of the nerve distal to the carpal ligament elicits a normal response in comparison to the segment of nerve across the carpal tunnel. In 100 hands of 50 normal adults, palmar stimulation of the median sensory fibers at 7 cm was compared to that at the wrist (14cm). Mean values for latency, amplitude, and duration were obtained, and palm/wrist ratios were calculated. Fifteen patients with CTS and 6 with underlying peripheral neuropathy were studied. This technique is useful for diagnosing early CTS and also for identifying an underlying mild peripheral neuropathy, eg, in diabetes mellitus.