Normal values for sensory thresholds in the cervical dermatomes: a critical note on the use of Semmes-Weinstein monofilaments.

In many healthy subjects, sensory thresholds for touch using Semmes-Weinstein monofilaments appear to be higher than the 2.83 filament, which some authors have suggested as a screening instrument. The currently proposed normal values, the interpretation of results, as well as the calibration of the filaments are questioned. A normative study of 20 normal subjects using Semmes-Weinstein monofilaments was undertaken at a pain clinic in a university hospital. The main outcome measures were sensory thresholds (touch) in dermatomes C3 to C8. Per subject, 24 sites were tested and 50 sites in dermatome C5 left of one subject. The threshold distribution patterns were analyzed. The mean threshold expressed in log (10 x F; with F = force in milligrams) of all sites (n = 480) in normal subjects was 3.10 (95% confidence interval, 2.34-3.86). The mean threshold per subject was 3.10 (range, 2.70-3.50). The mean threshold of 50 sites in dermatome C5 left of one healthy subject was 3.22 (range, 2.42-4.02). In the study contained herein, sensory thresholds in the cervical dermatomes have been shown to be higher than the generally proposed normal values. The cervical dermatomes show thresholds from 0.13 to 8.47 mN. This concurs with other authors. Results depend on the testing method, which in this study was different from previous studies. The testing method must be described accurately. The distribution of thresholds within all tested sites, dermatomes, subjects, or even within one dermatome in one subject are comparable. Individual results have to be related to the mean of the subject to determine abnormality. Calibration of the monofilaments is important. When these terms are met, testing with Semmes-Weinstein monofilaments is an easy, reliable, and relatively inexpensive method of quantitative sensory testing and can be a useful tool in the process of rehabilitation.