The contribution of median-ulnar communications in diagnosis of mild carpal tunnel syndrome.

In six patients with characteristic symptoms of carpal tunnel syndrome, electrophysiologic studies were normal, except for an initial positive deflection of the thenar muscle action potential with median nerve stimulation at the elbow but not at the wrist. This phenomenon is only seen with coexistent carpal tunnel syndrome and median to ulnar nerve communication and suggests carpal tunnel syndrome is present in these patients. As normal electrophysiologic studies occur in carpal tunnel syndrome (up to 8%) and median to ulnar communications are common (15%-31%), this observed finding is of practical clinical importance in the diagnosis of mild carpal tunnel syndrome despite otherwise normal electrophysiologic studies.