Carpal tunnel syndrome and the Riche-Cannieu anastomosis: electrophysiologic findings.

Two cases of carpal tunnel syndrome with Riche-Cannieu anomalies are reported. Despite complete absence of a median nerve evoked compound muscle action potential from the thenar eminence, these patients had significant preservation of function and minimal muscle atrophy. Activation of the ulnar nerve at both the wrist and elbow generated easily obtainable compound muscle action potentials from the thenar eminence with initial negative onset. This observed preservation of function and electrophysiologic responses are best explained by the presence of a Riche-Cannieu anastomosis innervating the thenar eminence through branches from ulnar nerve. To our knowledge there has not been a report of similar cases in patients with profound carpal tunnel syndrome and a Riche-Cannieu anomaly. We review the clinical findings, the electrodiagnostic data, and the impact of a Riche-Cannieu anastomosis on advanced carpal tunnel syndrome.