Differences in frequency of finger tremor in otherwise asymptomatic mercury workers

Tremor was measured from the index finger during low force, position holding in 18 control subjects and 18 battery workers with low level exposure to mercury. All workers were asymptomatic on clinical neurological examination. No differences were found in average tremor amplitudes between the groups, but statistically significant abnormalities in tremor frequency distribution existed. Tremor power spectra in the group of mercury workers were shifted toward the higher frequencies and compressed into narrow frequency peaks. These results suggest that measurements of finger tremor that evaluate the frequency distribution can produce a higher diagnostic yield than traditional visual clinical judgement. The findings also confirm other reports that currently permitted exposures to mercury are associated with subtle but distinctive differences in tremor accompanying voluntary movement.