Of 438 patients with the presumptive diagnosis of carpal tunnel syndrome (CTS), 639 symptomatic extremities were studied electrophysiologically. In 8% of the median distal sensory latency was normal and, in 44%, the distal motor latency was also normal. With the median sensory nerve conduction velocity (SNCV) of the forearm taken as 100%, the percentage of SNCV slowing across the wrist was over 25% in all the extremities tested including those with normal sensory or motor latency. The amplitude of the compound muscle action potential (CMAP) of the abductor pollicis brevis (APB) muscle was significantly decreased in patients compared to normal values obtained in 175 normal controls. It was much smaller, especially, in the extremities with evidence of denervation in APB and with slowed motor nerve conduction velocity of the forearm. Forty per cent of the extremities demonstrated abnormal electromyographic findings including evidence of denervation in 21.7%. Denervation was detected more frequently in the extremities with marked prolonged distal sensory or motor latency. Among various electrophysiological parameters, measurement of the SNCV slowing across the wrist is one of the most useful parameters in detecting early change of CTS. The slowing in SNCV across the carpal tunnel in patients with CTS is especially helpful when more established, routine parameters fail to detect abnormalities.
|Original language||English (US)|
|Number of pages||14|
|Journal||Electromyography and Clinical Neurophysiology|
|State||Published - Jan 1 1985|
ASJC Scopus subject areas
- Clinical Neurology
- Physiology (medical)