NEUROPHYSIOLOGICAL INVESTIGATION OF HANDS DAMAGED BY VIBRATION - COMPARISON WITH IDIOPATHIC CARPAL-TUNNEL SYNDROME

Forty-seven men with numbness and paresthesiae in their hands after lo ng-term occupational exposure to vibrating hand-held tools were examin ed neurophysiologically and clinically. The vibration thresholds of th e finger tips were assessed and fractionated neurography of the median nerve motor and sensory fibres carried out. They were compared with c ontrol groups of healthy subjects and patients with idiopathic carpal tunnel syndrome. The patients exposed to vibration had major increases in their finger vibration thresholds, shown with both the Goldberg-Li ndblom vibrameter and the Lundborg vibrogram. They also had a moderate ly increased motor distal latency at the wrist, but significantly less than patients with idiopathic carpal tunnel syndrome. Similar changes were seen in the sensory conduction velocities from finger to wrist. Measurement of fractionated conduction velocity across the carpal tunn el showed a bimodal distribution; one group of patients exposed to vib ration had a significant reduction in conduction velocity similar to t hat in the genuine carpal tunnel syndrome, and one group had no locali sed affection at the carpal tunnel, suggesting more distal dysfunction at the level of palm or finger, or at the receptor level. A careful n europhysiological assessment of these cases is necessary before treatm ent is planned. It is particularly important to confirm median nerve d amage at the wrist level if the carpal tunnel ligament is to be sectio ned.