Vibrotactile perception thresholds in hands occupationally exposed to vibration: Interpretation of sensorineural loss

Abstract

The tactile performance of the hand is now known to be critically dependent on neural activity in one population of slow‐adapting (SAI) and two populations of fast‐adapting (FAI, FAII) mechanoreceptors. A technique has recently been developed to establish the sensitivity of these receptor populations at the fingertip from vibrational perception thresholds determined psychophysically with sinusoidal stimulation [A. J. Brammer et al., J. Hand Surg. 12A, 870–875 (1987)]. A comparison of data from 98 vibration‐exposed and 34 normal hands, all screened to exclude confounding factors, has revealed two patterns of abnormal threshold elevation. The first, involving similarly elevated thresholds at all frequencies (2–200 Hz), is indicative of sensorineural losses of similar magnitude in each type of receptor‐nerve system, and so is suggestive of peripheral nerve degeneration. The second pattern involves elevated thresholds at frequencies mediated only by one or sometimes two receptor types (commonly SAI and/or FAII). A mechanoreceptor‐specific mechanism is unlikely to occur within a nerve trunk, and so this frequency‐dependent pattern is suggestive of selective damage to the nerve endings.