Assessing the severity of the neurological component of the hand-arm vibration syndrome

In view of the observation in epidemiologic studies that the neurological component of the hand-arm vibration syndrome develops first, a conservative measure of the presence and progression of the syndrome may be obtained from the degree of numbness and loss of fine touch. Degraded tactile spatial resolution, as measured by step and gap detection with an esthesiometer, has been found, on the average, in stages 2 and 3 of the Taylor-Pelmear classification for vibration-induced white finger (VWF). Present evidence suggests that this occurrence is due to the degeneration of slowly adapting (type I) and, possibly, fast adapting (type I) mechanoreceptors, and/or their nerve fibers. The apparatus commonly employed for measuring vibrotactile perception thresholds in clinical studies records the sensitivity of fast adapting type II mechanoreceptors (pacinian corpuscles), which play no role in step or gap detection. They may, however, provide early evidence of neurological changes occurring in the syndrome, as a significant degradation in the threshold of fast adapting type II receptors appears to develop, on the average, before stage 2 of VWF.