Minimal electrical stimulation intensity and duration to elicit maximal cutaneous silent period in hand

The cutaneous silent period (CSP) is an interruption of electromyographic activity produced by a painful stimulation delivered in homotopic cutaneous territory. It may be useful in evaluating small afferent fibers. However, standardized parameters of stimulation still need to be carefully defined before using this technique in routine clinical application. In this study, we investigated the effects of stimulus intensity and duration on the CSP.

Twenty healthy adults were included. The digital cutaneous nerve of the right index finger was stimulated and the CSP was measured from the right thenar muscle. The voluntary contraction of thenar muscle was maintained at 50% of maximal voluntary contraction, and the digital cutaneous nerve was stimulated using 0.1, 0.2, 0.5, and 1.0 ms durations and, for each stimulus duration, intensities increasing from 30 to 80 mA in 10 mA steps.

CSP duration first increased with increasing stimulus intensity and duration and then reached a plateau. Maximal CSP duration ranged from 34.7 to 71.0 ms (mean +/- S.D.: 51.2 +/- 9.5 ms). CSP duration was not significantly different for intensities varying between 40 and 80 mA and for stimulus durations varying between 0.2 and 1.0 ms.

This study demonstrates a high inter-individual variability of maximal CSP duration, and that CSP duration first increased with stimulus intensity and duration and then reached a plateau. We suggest to use a minimal stimulus intensity of 40 mA, and a minimal stimulus duration of 0.2 ms in order to elicit maximal CSP duration.