Objective: To assess whether occupational exposure to the solvent trichloroethylene (TCE) is associated with increased risk of Parkinson’s disease (PD).

Background: Severe solvent intoxication can rarely cause an acute parkinsonian syndrome, but epidemiologic studies of solvent exposure and PD risk are inconsistent. A PD cluster was previously identified in manufacturing workers exposed to the common degreasing solvent TCE, and TCE induces specific PD-like neuropathology in an animal model [1]. Our group reported increased risk associated with occupational exposure to TCE in a study of twins discordant for PD [2]. We sought to replicate this finding in a second population. 

Methods: We recruited PD cases and matched controls from North American movement disorders centers (SOLVENTS study). Occupational interviews collected information about industry/tasks/processes/materials for jobs since age 10. A blinded industrial hygienist and preventive medicine physician estimated TCE exposure likelihood (none, possible, probable), intensity (low, >low) and duration (hours/year*years), and estimated cumulative exposure. We pooled SOLVENTS with a prior case-control study in a large male twin cohort (TWINS study) that used identical exposure rating procedures. We assessed risk using generalized estimating equations adjusting for age, smoking, study, and twin-relatedness.

Results: 492 PD/481 controls in SOLVENTS, and 155 PD/117 controls in TWINS had complete data. 22 in SOLVENTS (21 male) and 15 in TWINS had any occupational exposure to TCE. PD risk was higher for any TCE exposure in SOLVENTS (odds ratio (OR) 1.4, 95%CI 0.6-3.3), TWINS (OR 3.1, 95%CI 0.9-10.5) and in pooled analyses (OR 1.8, 95%CI 0.9-3.7). In cumulative tertile pooled analyses restricted to men, relative to no exposure, OR for TCE exposure was 1.15 (0.5-2.6) for low (n= 12 in SOLVENTS, 9 in TWINS) and 3.6 (0.97-13.4) (n= 9 in SOLVENTS, 6 in TWINS) for high exposure (p-trend 0.05).

Conclusions: Although statistical power is limited and exposure assessment imprecise, our finding of a dose-response relationship supports observations in animal studies and suggests that occupational exposure to TCE may increase PD risk. Future work will investigate interactions with polymorphic variants in genes involved in TCE metabolism.

References: 1. Liu M, Choi DY, Hunter RL, Pandya JD, Cass WA, Sullivan PG, Kim HC, Gash DM, Bing G. Trichloroethylene induces dopaminergic neurodegeneration in Fisher 344 rats. J Neurochem 2011;112:773-83.

2. Goldman SM, Quinlan PJ, Ross GW, Marras C, Meng C, Bhudhikanok GS, Comyns K, Korell M, Chade AR, Kasten M, Priestley B, Chou KL, Fernandez HH, Cambi F, Langston JW, Tanner CM. Solvent exposures and Parkinson disease risk in twins. Annals of Neurology 2012;71:776-84.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/occupational-trichloroethylene-exposure-and-parkinsons-disease-risk/