Variations in dorsomedial hand innervation. Electrodiagnostic implications.

Sensory potentials recorded from the dorsal cutaneous branch of the ulnar nerve (DCUN) help localize ulnar nerve lesions. This conduction technique was first described by Jabre in 1980. Abnormalities detected with this technique in control populations are commonly attributed to local trauma. Anatomic variations of cutaneous innervation to the dorsum of the hand, however, have been described. We recorded DCUN responses using both the normal DCUN stimulation point and a secondary site of stimulation at the radial aspect of the forearm in 44 patients. Eleven patients demonstrated a low-amplitude DCUN response. Four of the 11 patients demonstrated sensory potentials obtained from the routine recording site of the DCUN with radial stimulation. We conclude that an abnormal DCUN response may represent anomalous innervation. To avoid some errors in localization, radial forearm stimulation should be performed whenever the DCUN response is abnormal.