Electrophysiological evidence of the Riche–Cannieu anastomosis in the hand and its diagnostic implications; 2 case reports

Introduction Anomalous anastomoses between the nerves of the hand are not as rare as thought to be. Amongst these, the Riche–Cannieu anastomosis (RCA) is a connection between the ulnar nerve and median motor nerve in the palm. Presence of this can sometimes be misdiagnosed as a severe median mononeuropathy at the wrist/carpal tunnel syndrome (CTS). We describe two cases that were referred for evaluation of CTS and were found to have incidental RCA. Results Electrophysiological studies showed typical findings consistent with RCA and coexistent mild CTS. Patients in whom median sensory and motor latency prolongations suggest CTS, the presence of an anastomosis should be suspected if the median motor amplitudes are worse than the median sensory amplitudes. Conclusion The electrophysiological study should be extended to avoid erroneous interpretation of low median motor amplitudes as severe CTS and to prevent unnecessary surgical intervention.