Thermotactile threshold testing for the evaluation of sensory nerve function in vibration-exposed patients and workers.

OBJECTIVES: The aim of the present study was to ascertain the usefulness of thermotactile testing under the measuring conditions clarified by our previous study in the evaluation of vibration-induced neuropathy.
METHOD: Thermal (warm and cold) thresholds were examined on the index fingers of both hands of ten patients with hand-arm vibration syndrome, 36 workers exposed to hand-transmitted vibration, and ten healthy controls, using an aesthesiometer under the following measuring conditions: change rate of the applicator temperature was fixed at a rate of 1 degrees C/s; finger contact force on the applicator was kept at 0.5 N; and forearm was positioned on a support. Vibrotactile thresholds at 125 Hz and pain thresholds were also measured on the index fingers.
RESULTS: Both warm and cold thresholds had more severely deteriorated in the patients than in the controls. Vibrotactile and pain thresholds were also increased in the patients. In the vibration-exposed workers, the neutral zone between the warm and cold threshold differed from in the controls. Thermotactile thresholds were likely to have deteriorated with advanced nerve impairment. Likelihood ratios of thermotactile testing were significantly high between the patients and the controls. For vibration-exposed workers with elevated vibrotactile and pain thresholds, the ratios were also significantly high, particularly in the neutral zone, though the accuracy tended to be lower than in the patients. Thermotactile thresholds appeared to be more closely correlated with pain thresholds than vibrotactile thresholds.
CONCLUSIONS: Thermotactile threshold testing under the present measuring conditions can be useful for evaluating small sensory nerve fibre dysfunction in vibration-exposed subjects, and the neutral zone may be a sensitive indicator in vibration-exposed workers who may have slight or mild nerve impairments.