Ulnar neuropathy at Guyon's canal: electrophysiological and surgical findings.

Published correlations between electrophysiological and surgical findings are relatively rare in cases of ulnar nerve compression at the wrist, compared to the more common compression of the ulnar nerve at the elbow. We describe a patient who presented with clinical and electrodiagnostic findings of a pure motor ulnar neuropathy involving the territory of the deep branch. Surgical exploration revealed that a ganglion cyst caused compression of the deep ulnar motor branch at Guyon's canal. This case illustrates the usefulness of electrodiagnostic studies in the localization of nerve entrapment prior to surgery.