Clinical results in severe carpal tunnel syndrome and motor nerve conduction studies.

The purposes of this study were to assess the value of motor nerve conduction studies as a prognostic indicator for severe carpal tunnel syndrome (CTS) and to investigate residual nerve disorder after surgery. Fifty hands in 46 patients with severe CTS were followed for at least 6 months after surgery for open carpal tunnel release. Compound muscle action potential (CMAP) from the abductor pollicis brevis (APB) muscle and the second lumbrical (SL) muscle were recorded before and after surgery, and distal latency (DL) and amplitude were analyzed. APB-CMAP was not recordable in 43 hands while SL-CMAP was recordable in all 50 hands before surgery. Results were excellent in 28 hands, good in 16 hands, fair in 6 hands, with no poor results after surgery. The ratio of excellent result was 65% in patients in whom DL of preoperative SL-CMAP was less than 10 ms, and 20% in patients whose DL was 10 ms or more. Delayed DL was seen in postoperative APB-CMAP and SL-CMAP, especially in the patients with good or fair results. We consider that SL-CMAP was valuable as a prognostic indicator for severe CTS, and if DL was 10 ms or more, myelinization of fibers would not be sufficient after surgery.