Vibration-induced multifocal neuropathy in forestry workers: electrophysiological findings in relation to vibration exposure and finger circulation

Objectives: To investigate neural conduction in the upper limbs of symptoma tic forestry workers with and without exposure to hand-transmitted vibratio n. A further aim was to assess the possible relationships between vibration exposure, nerve conduction and finger circulation in the forestry workers who used chain saws. Methods: A detailed neurophysiological investigation w as performed on the upper extremities of 20 chain saw workers, 20 forestry operators with heavy manual work but without vibration exposure, and 20 hea lthy male controls. All subjects were screened to exclude polyneuropathy. M easurements of sensory and motor nerve conduction (velocity and amplitude) were obtained bilaterally from the median, ulnar and radial nerves. To asse ss peripheral vascular function, the forestry workers underwent a cold test with plethysmographic measurement of finger systolic blood pressure (FSBP) . In the chain saw operators, vibration exposure was evaluated according to the International Standard ISO 5349. Indices of daily vibration exposure a nd lifetime cumulative vibration dose were estimated for each chain saw ope rator. Results: Sensory nerve conduction in several segments of the median and radial nerves was significantly reduced in the chain saw operators comp ared with that in the workers doing heavy manual work and the controls. The neurophysiological pattern more frequently observed in the chain saw opera tors was a multifocal nerve conduction impairment to several neural segment s with predominant involvement of sensory rather than motor fibres. Sensory nerve conduction velocities in the hands of the chain saw operators were i nversely related to both daily and lifetime cumulative vibration exposures. In the vibration-exposed forestry workers, neither were sensori-motor comp laints associated with vascular symptoms (finger whiteness) nor were electr ophysiological data related to cold-induced changes in FSBP. Conclusions: E xposure to hand-transmitted vibration, in addition to ergonomic stress fact ors, can contribute to peripheral nerve disorders occurring in forestry wor kers who operate chain saws. The findings of this study suggest the existen ce of an exposure-effect relationship for vibration-induced neuropathy. Dif ferent underlying mechanisms are likely to be involved in the pathogenesis of the neurological and vascular components of the hand-arm vibration syndr ome.