[Electrophysiological diagnosis in ulnar nerve entrapment at elbow]

Using "inching technique" we recorded antidromic sensory nerve action potentials from the little finger and compound muscle action potentials from the abductor digiti minimi, first dorsal interosseous and flexor carpi ulnaris muscles in 30 entrapped ulnar nerves. In cubital tunnel syndrome, localized conduction delay occurred most commonly at a point 2 to 4 cm distal to the medial epicondyle. In other ulnar neuropathies, with the exception of cubitus valgus deformity, conduction block or delay was noted at a site just distal to the medial epicondyle. These conduction abnormalities were most commonly observed in the abductor digiti minimi and first dorsal interosseous. In contrast, conduction abnormality in tardy palsy secondary to the valgus deformity reflected mainly in the flexor carpi ulnaris. This method provides useful information in diagnosing the early involvement and precise localization of nerve entrapment, and differentiation of cubital tunnel syndrome from other ulnar nerve entrapment.