Parkinson Disease and Exposure to Trichloroethylene: More Suggestive Data

Occupational exposure to the industrial solvent trichloroethylene increases the risk of Parkinson disease, according to researchers at the Parkinson's Institute and Clinical Center. The California-based, nonprofit organization released its study findings, which have not been presented at a scientific meeting or peer reviewed, on Sunday—apparently by way of press release. The data are scheduled to be presented at the annual meeting of the American Academy of Neurology in April.

According to sources picking up news of the study, data from 198 twin pairs in the World War II Veteran Twins Cohort Registry showed that the risk of PD in individuals with probable exposure to the solvent* was more than 5 times that of twins without probable exposure.** In a MedPage Today piece, an odds ratio (5.5) is reported, but no frequency rates of disease are provided. Also the 95% confidence interval for the odds ratio is very wide (1.02, 30)—indicating that the accuracy of the measured risk is uncertain.

Interest in trichloroethylene exposure as a risk factor in PD extends back to the early 90s, when it was reported by German investigators that a metabolite of the solvent is chemically similar to the neurotoxin MPTP. (The metabolite of MPTP, MPP+, has a predilection for the dopamine-producing neurons of the substantia nigra—the area of the brain that is primarily affected in PD. The MPTP story, itself, is fascinating and the subject of an excellent Nova episode, "The Case of the Frozen Addict," from 1986.)

In 2008, researchers at the University of Kentucky published their study of 30 industrial workers with PD or parkinsonism, who had long-term exposure to trichloroethylene. The study authors suggested that a worker's proximity to the solvent was related to his risk of the movement disorder. These findings were complemented by animal studies, which showed that oral intake of trichloroethylene for 6 weeks resulted in the degeneration of brain areas that are typically affected in PD.

* Presumed on the basis of occupation (eg, aircraft mechanic, electrician).

** The study of twins (and presumably, these are identical twins) largely eliminates any potentially confounding genetic risks of Parkinson disease.

Image of 1886 drawing of PD patient by neurologist Sir William Richard Gowers at Wikimedia Commons.