Introduction.
There are various anomalous communications between the ulnar and median nerve in both forearm and hand. Nevertheless, since many anastomosis are asymptomatic, they are often undiscovered until nerve injuries occur. Marinacci anastomosis, the unification of ulnar nerve and median nerve at forearm and Riche-Cannieu anastomosis, communication between the deep branch of ulnar nerve and the recurrent branch of median nerve in the hand, are some of the examples of rare anomalies. This case report describes electrophysiological feature of ulnar neuropathy at the elbow in patient with double ulnar-to-median nerve anastomoses.
Case presentation.
A 75-year old male was referred for electrodiagnostic study (EDX) with chief complaints of paresthesia in the medial aspect of the right forearm. The symptom started 2 months ago and there was no history of trauma or neck pain.
On physical examination, there was sensory loss in the right forearm along the ulnar sensory nerve distribution. Tinel sign was positive at the right cubital tunnel and strengths of all the upper extremity muscles, including right hand were intact.
In the nerve conduction study, low amplitudes were shown in compound muscle action potential (CMAP) of the right ulnar nerve with abductor digiti minimi muscle recording and sensory nerve action potential (SNAP) of the right ulnar and dorsal ulnar cutaneous nerves. In needle electromyography (EMG), fibrillation potentials and positive sharp waves (F&P) and polyphasic motor unit action potentials (MUAP) with reduced recruitment patterns were noted in the right ulnar nerve innervated muscles. Findings were compatible with right ulnar neuropathy at the elbow.
However, further electrophysiologic findings were suspicious of anomalous communication between the ulnar and median nerve. Amplitude of the right median CMAP was very low while amplitude of the right median SNAP was within normal limit. In needle EMG, F&P but normal MUAP were noted in the flexor pollicis longus, pronator quadratus and abductor pollicis brevis (APB) muscles. No F&P were noted in other median nerve innervated muscles and C8 myotomes. In ulnar nerve stimulation with APB recording, CMAP without initial positive deflection was obtained in both wrist and below-elbow stimulations. The possibility of median neuropathy, cervical radiculopathy or brachial plexopathy were ruled out and the patient was finally diagnosed as incomplete ulnar neuropathy at the elbow with ulnar-to-median anastomosis. Based on electrophysiologic findings, we assumed that there would be two communication branches, one in the forearm (connection to anterior interosseous nerve) and the other in the hand (connection to recurrent branch of the median nerve), respectively.
Conclusion.
The presence of these anastomosis may complicate the interpretation of electrophysiological findings and result in misdiagnosis, coexisting anterior interosseous neuropathy and median neuropathy at the wrist. |
