Electrophysiological Features of Ulnar Tunnel Syndrome Caused by Ganglion–A Descriptive Study

Objective: Ulnar tunnel syndrome (UTS) is an uncommon ulnar neuropathy. Clinical and electrophysiological diagnosis of UTS is difficult. The purposes of this study were to assess the diagnostic value of the nerve conduction measurements for UTS caused by ganglion, and to investigate the electrophysiological features of UTS. Methods: The subjects were five patients with UTS. Before surgery, all patients had motor weakness and intrinsic muscle atrophy with positive Froment’s sign, and three patients had numbness and hypesthesia in the ulnar nerve distribution. In all patients, a magnetic resonance imaging (MRI) of the wrist demonstrated soft tissue mass at the ulnar tunnel. The compound muscle action potential (CMAP) from the abductor digiti minimi (ADM) muscle and the first dorsal interosseous (FDI) muscle, and sensory nerve action potential (SNAP) from the little finger were recorded and analyzed. All patients underwent surgery of ulnar tunnel release and excision of the ganglion. Static 2 points discrimination tests (2PD) on the little finger, pinch strength were assessed before and after surgery. Results: ADM-CMAP and FDI-CMAP were recorded in all five patients and they all showed abnormality in ADMand FDI-CMAP. Delayed latency (mean: 5.4 msec) and / or low amplitude (mean: 1.4mV) were seen for ADM-CMAP and for FDI-CMAP (mean: 7.1 msec, 2.6 mV). SNAP was recorded in four patients and it all showed normal latency and amplitude. After surgery, all patients obtained complete recovery of motor function and sensation. Mean 2PD improved from 7.8 mm to 5.0 mm, and mean pinch strength increased from 1.8 kg to 4.8 kg postoperatively. Postoperative ADM-CMAP and FDI-CMAP showed the shortening of latency and the increase of amplitude, but they did not recover to the normal range. Conclusion: Both ADM-CMAP and FDI-CMAP were important for definite electrophysiological diagnosis of ulnar tunnel syndrome caused by ganglion. Residual delayed latency and low amplitude were seen after surgery regardless of complete recovery of intrinsic muscle.