Median-ulnar nerve communications: electrophysiological demonstration of motor and sensory fibre cross-over.

In a 33-year-old female with carpal tunnel syndrome the presence of anomalous communications between median and ulnar nerves was electrophysiologically demonstrated in the forearm. Motor latencies from proximal and distal stimulation sites along the median nerve fibres to the abductor pollicis brevis were identical. Proximal latency "increased" after procaine infiltration of the ulnar nerve at the wrist. Normal latency to the abductor digiti minimi was obtained on stimulation of the median nerve at the elbow. Along the sensory fibres of the median nerve orthodromic conduction velocity was markedly slowed from digit III to the wrist and normal from the wrist to the elbow. On supramaximal stimulation of digit III a sensory response was also recorded from the ulnar nerve at the wrist. On stimulation of digit V a sensory potential was recorded from the median nerve at the elbow. This appears to be the first electrophysiological demonstration of an anomaly involving both the motor and sensory fibres of both the median and the ulnar nerves.