A new median motor test: comparison with conventional motor studies in carpal tunnel syndrome

Carpal tunnel syndrome (CTS) is the most commonly operated of entrapment peripheral neuropathies, and its surgical outcome largely depends on the underlying mechanism involved. Early identification of CTS is essential because it is associated with a better prognosis.

To identify CTS at an earlier stage and hence improve the potential future outcome, the authors propose incorporating a new method of using the second lumbricalis (2L-MC) to register the nerve conduction.

We prospectively evaluated 121 of 216 patients with confirmed carpal tunnel syndrome and 49 cases from 25 healthy subjects. According to the accepted criteria of Stevens, we divided our study into two groups of mild CTS and moderate CTS, respectively. Following our proposed method, we stimulated the palm, distal forearm, and elbow and measuring the difference in latency between the second lumbricalis and the second interosseous, in addition to the conventional neurophysiologic assessments.

Seventeen of 109 (15.6%) hands showed a significant difference in latency using 2L-MC within the mild CTS group, while only 4 of 107 (3.7%) within the moderate CTS group remained undiagnosed using this method. In the mild CTS group, motor involvement was only shown to be slightly more sensitive when compared with 2LI-DML.

Adding the proposed test to the conventional studies of CTS in our cases presented showed a 14% increased sensitivity in detecting motor dysfunction when compared with conventional studies alone. Therefore, this new 2L-MC study represents a useful technique for assessing early motor involvement in CTS and would only add a few extra minutes to the standard diagnostic procedures. To conclude, we propose that incorporating this study as part of the standard assessment of CTS is given further consideration.