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

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 49.9 m/sec), 2 (14%) had an SP. Of 15 arms with moderate slowing (MMFCV of 43.0 to 46.9 m/sec), 7 [corrected] (46%) had an SP. Of 9 arms with severe slowing (MMFCV of < 43.0 m/sec), 4 (44%) had an SP. The frequency of SPs for 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 (< 47.0 m/sec) should prompt a careful electrophysiologic investigation to exclude an SP.