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Updated: Sep 25, 2026
Metacarpal Small Incision for Carpal Tunnel Syndrome
Published on: April 5, 2024
The reason for forearm conduction slowing in carpal tunnel syndrome: an electrophysiological follow-up study after
Ming Hong Chang1, Shiew Jue Wei, Lee Wei Chen
1Section of Neurology, Taichung Veterans General Hospital, No. 160, Chung Kang Road, Section 3, 40705, Taichung, Taiwan, ROC. cmh50@ms10.hinet.net
Background:
The exact cause of decreased forearm median motor conduction velocity (FMMCV) in carpal tunnel syndrome (CTS) is still a subject of controversy. A conduction block or an axonal loss in the large myelinating fibers upon wrist compression, or retrograde axonal atrophy, is suspected.
Methods:
In order to attempt a determination of the cause, 10 patients with clinical symptoms and signs of CTS, confirmed using standard electrodiagnosis and with a slowed FMMCV <50m/s, were included in this study. Serial standard median motor conduction studies were performed at baseline, 1 week, 2 weeks, 4 weeks, 8 weeks, and 12 weeks after endoscopic ligament release. Serial median motor distal latencies (MMDL), compound muscle action potential (CMAP) amplitudes, and FMMCV, were determined and compared.
Results:
Significant improvement in MMDL had occurred at the 1-week follow-up examination; however, no such improvement in FMMCV was observed. Furthermore, a significant increase in CMAP amplitude was evidenced beginning 4 weeks after surgery. The results revealed an improvement in median motor conduction, across the wrist segment, that did not parallel the increase in FMMCV, suggesting that a conduction block or axonal loss at wrist compression was not the likely cause of the decreased FMMCV.
Conclusions:
Retrograde axonal atrophy, not selective damage to the large myelinating fibers at the wrist, is the direct cause of decreased FMMCV in CTS.
