DIFFERENTIAL LATENCY TESTING - A MORE SENSITIVE TEST FOR RADIAL TUNNEL-SYNDROME

A modification of the standard electrodiagnostic test was developed in an effort to provide a more sensitive electrodiagnostic evaluation in radial tunnel syndrome. Radial motor nerve latency recordings were ob tained in 3 different forearm positions. neutral, passive supination, and passive pronation. The maximal difference in these recordings, the differential latency, in 25 patients with radial tunnel syndrome of g reater than 6 months duration (test group) was compared with those in 25 asymptomatic volunteers (control group). Differential latency recor dings were obtained in all patients in the test group before and after surgery. Radial nerves that were compressed demonstrated a significan tly greater differential latency (0.44 +/- 0.12 ms) versus controls (0 .12 +/- 0.008 ms). Following radial nerve decompression, differential motor latencies in the test group decreased below control values, demo nstrating a resolution of the provoked electrical response with a post operative differential latency of 0.07 +/- 0.05 ms. Our results demons trate the differential motor latency of the radial nerve to be a sensi tive electrodiagnostic tool in patients with radial tunnel syndrome. A differential latency of greater than or equal to 0.30 ms was consider ed indicative of radial tunnel syndrome. Copyright (C) 1998 by the Ame rican Society for Surgery of the Hand.