Power spectrum analysis of compound muscle action potential in carpal tunnel syndrome patients.

The objective of using wave-form analysis to assess compound muscle action potential (CMAP) in entrapment neuropathy had not been fully developed. We applied the power spectrum analysis to patients with carpal tunnel syndrome (CTS) for this purpose. 24 patients with CTS were divided into three stages according to Mackinnon s classification, and 50 normal volunteers were examined. CMAP was obtained from the abductor pollicis brevis with supramaximal stimulation to median nerve. Mean and peak frequencies were measured by power spectrum analysis. The distal latencies of CMAP and the sensory nerve conduction velocities showed some prolongation in CTS patients. Integral values of CMAP were also decreased in CTS patients. Mean and peak frequencies of power spectrum of CMAP in volunteers were 134 Hz and 98 Hz, respectively. These values shifted into lower frequencies in CTS patients, namely 102 Hz and 61 Hz. Regardless of clinical stage, distal latency of CTS patients correlated with mean frequency.