Transcarpal Motor Conduction Velocity: Repeatability and Application in Carpal Tunnel Syndrome.

Background: Conduction velocity of the short segment of the median motor nerve, across wrist (transcarpal motor conduction velocity (TCMCV)), has been used to increase diagnostic yield in carpal tunnel syndrome (CTS). However, repeatability of this parameter has not been studied till date. It has not been used as an indicator of response to treatment. Using surface stimulation techniques, it is difficult to localize the sites of stimulation of transcarpal segment of median nerve in palm. As a result, small errors in measurements of TCMCV can be magnified and variability of TCMCV may occur on successive measurements. Despite this possible variation, TCMCV can be a useful tool for assessing response to therapy, if its repeatability is assessed and a cut-off value determined for a significant change in nerve conduction velocity.

Purpose: In this study, it was determined whether TCMCV is repeatable. If found to be repeatable, we show a method to determine the cut-off value of the change in this parameter for it to be considered significant.

Methods: Difference between values of TCMCV on successive measurements was obtained in hands of 26 controls. Repeatability of this parameter was determined in this control population following criteria of British Standards Institution. In 19 patients of CTS, treated with intracarpal steroid injection, pre-treatment and post-treatment values of TCMCV, and of symptom severity scale (SSS) and functional status scale (FSS), were obtained at 1, 2, and 3 months after treatment.

Results: Repeat measurements of TCMCV were made in each hand of all controls. After applying criteria of British Standards Institution, to such recordings, TCMCV was found to be repeatable and the cut-off value for significant change determined. According to this cut-off value, 4 patients of CTS showed improvement in TCMCV, with consistent improvement in SSS and FSS. Change in TCMCV corroborated qualitatively with changes in SSS and FSS.

Conclusion: Repeatability of TCMCV can be assessed by criteria of British Standards Institution and a cut-off value determined to use it as an indicator of response to treatment in CTS.