Forearm velocity in carpal tunnel syndrome: When is slow too slow?

Abstract

Objective: To correlate the frequency of superimposed processes (SPs) such as radiculopathies, polyneuropathies, and plexopathies with median motor forearm conduction velocity (MMFCV) in patients with carpal tunnel syndrome (CTS). Design: All cases of diagnosed CTS were retrospectively analyzed for evidence of SPs. Setting: Electrophysiology laboratory of a tertiary care center. Participants: One hundred fifty-five patients (44 men, 111 women), ages 19 to 94, who were referred for and met electrophysiologic criteria for CTS, both with and without MMFCV slowing. Main Outcome Measure: The frequency of SPs in patients with no, mild, moderate, and severe MMFCV slowing. Results: A total of 192 arms from 155 patients were studied. Of 14 arms with mild slowing (MMFCV of 47.0 to 49.9m/sec), 2 (14%) had an SP. Of 15 arms with moderate slowing (MMFCV of 43.0 to 46.9m/sec), 4 (46%) had an SP. Of 9 arms with severe slowing (MMFCV of <43.0m/sec), 4 (44%) had an SP. The frequency of SPs in both the moderate and severe groups was significantly higher than that in patients with a normal MMFCV (p < .01); of 154 arms with a normal MMFCV, only 9 (6%) had an SP. Conclusion: In cases of CTS, the finding of moderate to severe slowing of MMFCV (<47.0m/sec) should prompt a careful electrophysiologic investigation to exclude an SP.