Organochlorine pesticide exposure in essential tremor: A case-control study using biological and occupational exposure assessments

Essential tremor (ET) is a common neurological disorder. Its etiology and pathogenesis are not well understood and several environmental factors (i.e., toxicants) have been studied. Organochlorine pesticides (OCPs) are potent tremor-producing chemicals. These pervasive environmental contaminants have been linked with other tremor disorders (e.g., Parkinson's disease) but they have not been assessed in ET cases. Our objective was to test the hypothesis that ET is associated with OCP exposure. Serum OCP concentrations and lifetime occupational histories were assessed in ET cases and control subjects. Six serum OCP concentrations (p,p′-DDE, p,p′-DDT, β-hexachlorocyclo-hexane, oxychlordane, trans-nonachlor, and dieldrin) were assessed. Data from a lifetime occupational history were reviewed by a blinded industrial hygienist. The six serum OCP concentrations were similar in 136 ET cases and 144 control subjects. There was no association in ET cases between the six serum OCP concentrations and total tremor score. Three (2.2%) ET cases versus 9 (6.3%) controls had past occupational exposure to OCPs (OR = 0.34, 95% CI = 0.09-1.28, p = 0.10). Although OCPs have been associated with other tremor disorders, we were not able to find an association between the six most tremorogenic OCPs and ET. Our data suggest that these tremor-producing chemicals are not of major etiological importance in our patients with ET.