Multifocal neural conduction impairment in forestry workers exposed and not exposed to vibration

The aim of the study was to assess peripheral neural involvement induced by exposure to hand-arm vibration.

Twenty lumberjacks, working regularly with chain-saws and exposed to hand-arm vibration (group E) and 20 forestry workers performing heavy manual work and not exposed to vibration (group NE) were matched with a control group of 20 healthy non-manual workers (group C). The subjects of groups E and NE, all symptomatic, and of group C underwent extensive bilateral neurophysiological examination consisting of: sensory conduction (velocity and amplitude) of radial, median and ulnar nerves in digit-wrist segments; sensory conduction (velocity) of median nerve in wrist-elbow segment; mixed conduction (velocity and amplitude) of median and ulnar nerves in palm-wrist segments; motor conduction velocity, including distal motor latencies, and amplitude of median (elbow-wrist) and ulnar (elbow-wrist and across the elbow) nerves.

Electrophysiological abnormalities were found in 85% of group E's limbs, versus 62.5% of group NE's limbs. The most frequent pathological pattern in group E was a 'multifocal' impairment (multiple sites of several nerve segments), with a prevalent involvement of sensory rather than motor fibres in the hand, seldom extending to the forearm. Multivariate analysis showed that the neurographic parameters which better characterized workers exposed to hand-arm vibration had a pattern different from that usually found in idiopathic carpal tunnel syndrome (CTS).

These results suggest that vibration-induced neural involvement can be considered neither pure digital neuropathy, nor definite CTS, as previously described.