Electrodiagnostic characteristics of acute carpal tunnel syndrome.

Carpal tunnel syndrome (CTS) exemplifies a cumulative trauma disorder which may occur in industrial settings. Occasionally, industrial workers develop CTS acutely over the course of a few days to a few weeks. We recently performed electrodiagnostic studies on 22 workers at a midwestern automobile manufacturing plant who developed symptoms compatible with CTS. All tests were within eight weeks of symptom onset; 70% were within four weeks. The acute syndrome was manifested by a conduction block of sensory, motor, or both fiber types beneath the carpal ligament. All patients received sensory studies; nine had motor studies as well. Sensory nerve latencies were not prolonged in proportion to the symptoms, which were short in comparison to the low amplitude sensory nerve action potential evoked proximal to the carpal ligament. Sensory nerve action potential amplitude at midpalm averaged 200% of the value obtained proximally. Because of short distance and residual latency, comparison of motor latencies proximal and distal to the carpal ligament was less helpful than the difference in amplitude of the evoked potentials. Amplitude of the distal response increased an average of 32%. Prompt identification of acute CTS was followed by a recommendation for job change which, along with conservative therapy, led to resolution of symptoms in 77% of patients. The diagnosis of acute CTS leading to avoidance of inciting activities is beneficial in the industrial setting.