Tremor frequency patterns in mercury vapor exposure, compared with early Parkinson's disease and essential tremor

A new portable tremometer allows determination of tremor intensities at dif ferent tremor frequencies. Based on past studies, two tremor frequency wind ows of similar size were chosen at 3.0-6.5 Hz and 6.6-10.0 Hz to reflect ma jor tremor intensities in Parkinson's disease and mercury vapor poisoning, respectively. In 81 healthy controls, total tremor intensity was higher for the preferred hand and depended on age. Ten patients treated For Parkinson 's disease showed substantially increased tremor intensity, especially with in the low-frequency window. This pattern was also apparent in 14 patients with de novo Parkinson's disease whose overall tremor intensity was only mi ldly elevated. In contrast, ten patients with essential tremor had peak fre quencies in both windows, and some patients had increased tremor on one sid e only. Sixty-three Brazilian gold traders exposed to mercury vapor showed increased tremor predominantly in the high-frequency window. Three of the g old traders had a narrower tremor peak at frequencies of 7-8 Hz. While the urine-mercury concentration was significantly associated with the current n umber of burning sessions per week, it did not correlate with tremor intens ities. However, eight traders had a urinary mercury excretion level above 5 0 mu g and at the same time a greatly increased average tremor intensity wi thin the high-frequency window. These patterns were statistically significa nt for relative tremor intensities, bur were less clear when total intensit ies were used. These observations suggest that the relative distribution of tremor intensities in specific frequency bands may be a valuable supplemen t to current diagnostic methods for subjects with mercury vapor exposure. ( C) 1999 Intox Press, Inc.