Solvents and the Risk of Parkinson's Disease
Abstract & Commentary
By Melissa J. Nirenberg, MD, PhD, Associate Professor, Neurology and Neuroscience, Weill Cornell Medical College.
This article originally appeared in the February issue of Neurology Alert. At that time it was peer reviewed by M. Flint Beal, MD, Anne Parrish Titzel Professor, Department of Neurology and Neuroscience, Weill Cornell Medical Center, New York, NY. Dr. Nirenberg and Dr. Beal report no financial relationships relevant to this field of study.
Synopsis: Exposure to specific solvents, and trichloroethylene in particular, is associated with an increased risk of Parkinson's disease.
Source: Goldman SM, et al. Solvent exposure and Parkinson disease risk in twins. Ann Neurol 2011; DOI:10.1002/ana.22629.
Parkinson's disease (PD) has been closely linked to both genetic and environmental factors. In prior studies, environmental exposures associated with PD have included pesticides, well water consumption, and residency in rural areas; inverse risk factors have included smoking and coffee use. Some studies have implicated solvents in PD risk, but data have been lacking about whether (and which) solvents may be involved.
In this study, the authors examined the potential association between PD and exposure to six specific solvents. They used a case-control study design, with 99 pairs of twins who were discordant for PD status. Study subjects, all of whom were male, were recruited from the National Academy of Sciences/National Research Council World War II Veteran Twins Cohort. Structured questionnaires were used to obtain detailed lifetime occupational and hobby histories from each subject. Expert raters, blinded to PD status, then used this information to infer each subject's lifetime exposure to these six solvents.
The authors found that ever exposure to trichloroethylene (TCE) was associated with an increased risk of PD (odds ratio [OR], 6.1; P = 0.034). There also were non-significant trends toward increased PD risk with ever exposure to perchloroethylene (PERC; OR, 10.5; P = 0.053) or carbon tetrachloride (CCl4; OR, 2.3; P = 0.088). There were similar findings when they examined the duration of exposure and cumulative lifetime exposure to these solvents. Based on these findings, the authors conclude that solvents, and TCE in specific, are associated with an increased risk of PD.
In this small but well-designed epidemiological study, the authors provide new evidence to support the association between solvent exposure and PD, with a significant association between PD and TCE, and similar trends for PERC and CCl4. Given that these solvents are commonly used in industry, dry cleaning, and household products, the findings have major public safety implications.
Study strengths include the population-based study design and use of twin pairs to minimize potential confounders. Limitations include the small sample size, retrospective study design, and inferred calculation of solvent exposure. In addition, the study sample consisted exclusively of male World War II veterans, such that the results may not be generalizable to other populations.
In summary, this study suggests that exposure to specific solvents may increase the risk of PD. Given the major public health implications of these findings, further studies in larger, prospective cohorts are warranted.