Electrophysiologic study of the Riche-Cannieu anomaly

A standard electrodiagnostic evaluation of an individual sustaining left upper extremity trauma suggested compromise of the ulnar nerve at the elbow associated with median nerve innervated thenar muscle membrane instability. A comprehensive electromyographic examination failed to document a cervical root or brachial plexus lesion to explain the denervation in both the thenar and hypothenar musculature. A detailed electrophysiologic investigation was performed to explore the possibility of an anomalous connection between the deep branch of the ulnar nerve and the recurrent median nerve. Intramuscular recording electrodes of the thenar and hypothenar region, combined with near nerve stimulation of the median and ulnar nerves at the elbow and wrist were employed to avoid volume conduction errors. Responses were obtained from the abductor pollicis brevis and opponens pollicis when both the median and ulnar nerves were stimulated. The median nerve was blocked at the wrist with a local anesthetic and ulnar nerve continued to produce responses in the thenar muscles. The patient underwent a medial epicondylectomy and all membrane instability subsequently resolved. This investigation documents electrophysiologically the often forgotten Rich-Cannieu anomaly and offers a pathophysiologic explanation for the so-called ulnar hand.