Diagnosis of ulnar neuropathy: a new approach.

Conventional electrodiagnosis used to detect an ulnar neuropathy at the elbow depends on accurate determination of ulnar nerve length across this segment. We present a new approach, using the difference in latency of the compound nerve action potentials (CNAPs) of the ulnar and median nerves elicited by stimulation at the wrist and recorded 10 cm above the elbow. Sixty normal controls were examined in order to determine the normal upper limit (1.4 ms) of the difference in CNAP latency of the ulnar and the median nerves (Dlat index). Values obtained in 10 patients with ulnar nerve lesions are discussed. This test was shown to be both sensitive and specific, was independent of ulnar nerve length, and was easy to perform.