356 - A Rare Electrodiagnostic Finding of Riche-Cannieu Anastomosis with Superimposed Carpal Tunnel Syndrome

Case Diagnosis:
Riche-Cannieu anastomosis (RCA) with superimposed severe Carpal Tunnel Syndrome

Case Description:
81 year-old male presenting with hand numbness, pain, and weakness on the first three digits. Physical examination demonstrated positive Tinel’s/Phalen’s signs without gross atrophy of thenar muscles. Electrodiagnostic studies(EDX) were requested for confirmation of carpal tunnel syndrome(CTS).


EDX showed bilateral dual innervation of abductor pollicis brevis(APB) muscles by median(MN) and ulnar nerves(UN) as well as bilateral severe MN entrapment at the wrists with denervation potentials on APB. RCA was demonstrated by activation of the UN at the wrist and elbow, while recording on APB, which generated distal and proximal compound muscle action potentials(CMAPs) from the thenar eminence with initial positive deflection despite marked decrement of MN CMAP amplitude with no thenar atrophy.



Discussions: RCA is usually an UN to MN connection of the hand involving mostly motor fibers. It is rarely seen when compared to the Martin-Gruber anastomosis. RCA with CTS can present as numbness, paresthesia, pain, and hand weakness. In RCA alone, there is no obvious thenar atrophy and EDX will show almost absent CMAP with sparing of median sensory nerves(SNAP) as motor fibers run with the UN. Rare cases can present as RCA with superimposed CTS in which there is dual innervation of the thenar muscles by the MN and UN through the anastomosis. EDX then could show no median SNAP and marked decrement or absence of median CMAP, and may show abnormal needle electromyogram findings in APB.




Conclusions: Clinical suspicion should be raised in patients presenting symptoms of severe CTS with abnormal median CMAP amplitude and mild or no atrophy of APB muscle on EDX. Knowledge of RCA is essential because it may result in incorrect diagnosis, EDX interpretation, and management in cases of MN entrapment at wrist, which could ultimately affect patients’ outcomes if not identified correctly.