Ulnar nerve involvement in carpal tunnel syndrome.

This is a retrospective study of the involvement of the ulnar nerve in patients with electrodiagnostic evidence of carpal tunnel syndrome as defined by median sensory nerve action potential (SNAP) greater than 3.6msec at the wrist and/or motor distal latency in excess of 4.3msec. The study included 248 patients, 63 (25%) with unilateral and 185 (75%) with bilateral carpal tunnel syndrome. The electrodiagnostic criteria for ulnar nerve involvement was a SNAP peak latency greater than 3.7msec and/or motor distal latency in excess of 4.2msec. One hundred fourteen patients (46%) had delayed ulnar SNAP peak at the wrist; of these, 100 cases had bilateral ulnar nerve involvement and 14 had unilateral abnormalities. Slowing of the motor nerve conduction velocity for the elbow-wrist segment was noted in 24% and 15% of the study group for the median and ulnar nerves, respectively. An incidental finding was the presence of "double crush syndrome" in 35 patients (14%). The results of this study suggest the frequent association of ulnar nerve involvement at the wrist for sensory fibers and carpal tunnel syndrome.