During the past decade several studies have explored causal factors for neurodegenerative diseases, including multiple sclerosis, systemic sclerosis, amyotrophic lateral sclerosis, and Parkinson’s disease.  Due to the rarity of these diseases, most of these studies have necessarily employed case-control design features.  Interestingly, several of these studies find apparent associations with occupational exposure to organic solvents.

In 2001, researchers at the Department of Public Health of the Medical College of Ohio published an article which investigated the causal association between solvent exposure and systemic sclerosis. Aryal, BK, et al., “Meta-analysis of systemic sclerosis and exposure to solvents,” Amer. J. Ind. Med. 40(3):271-274 (2001). The authors conducted a literature search for articles regarding solvent exposure and systemic sclerosis. They identified seven case-control studies and one cohort study published between 1989 and 1998 and conducted a meta-analysis of these epidemiologic studies. They found that the combined estimator of relative risk for all studies was 2.91, with a 95% confidence interval (CI) of 1.60 to 5.30. The combined estimator of relative risk for the seven case-control studies was 3.14 (95% CI, 1.56-6.33). The authors found that the risk of systemic sclerosis was increased about 3-fold in the studies and that this increase was statistically significant. The authors therefore concluded that organic solvent exposure is likely a cause of systemic sclerosis.

A review article regarding the association between organic solvents and multiple sclerosis was published by Swedish researchers in 1996. Landtblom, AM, et al., “Organic solvents and multiple sclerosis: a synthesis of the current evidence,” Epidemiology 7(4):429-33 (1996). These authors found 13 relevant studies which included information on solvent exposure. In 10 of the studies, there were indications of an increased risk of multiple sclerosis in relation to solvent exposure. The authors made three selections of studies for both pooled analyses and meta-analyses. The relative risk point estimates that they obtained varied from 1.7 to 2.6. The authors concluded their evaluation was consistent with the hypothesis that organic solvents cause multiple sclerosis.

A case-control study of patients suffering from amyotrophic lateral sclerosis (ALS) was conducted by researchers at the University of Washington at Seattle. McGuire, V., et al., “Occupational exposures and amyotrophic lateral sclerosis: A population-based case-control study,” Amer. J. Epidemiol. 145(12):1076-88 (1997). This study showed a statistically significant increase in ALS among men heavily exposed to agricultural chemicals (odds ratio 2.8 (95% CI 1.3-6.1).

In 2000, Italian researchers conducted a nested case-control study to investigate a causal association between organic solvent exposure and Parkinson’s disease. Pezzoli, G., et al., “Hydrocarbon exposure and Parkinson’s disease,” Neurology 55(5):667-73 (2000).  These researchers found that exposure to hydrocarbon solvents directly correlated to disease severity and concluded that occupations involving the use of hydrocarbon solvents are a risk factor for earlier onset of symptoms of Parkinson’s disease and more severe disease throughout its course.

In 2001, researchers affiliated with the European Study Group on Atypical Parkinsonisms investigated causality between organic solvent exposure and multiple system atrophy, a rare form of atypical Parkinsonism. Vanacore N, et al., “Epidemiology of multiple system atrophy,” Neurol. Sci. 22(1):97-9 (2001). These researchers noted that only one case-control study had been done of this rare disease and that the study showed an increased risk of MSA associated with occupational exposure to organic solvents, as well as plastic monomers, pesticides, and metals — all substances which involve the use of organic solvents.

Thus, the causal association between organic solvent exposure and development of neurodegenerative diseases is now well-supported by the epidemiologic literature.  In recent years, the Metzger Law Group has litigated several cases of workers who were occupationally exposed to organic solvents and unfortunately developed various neurodegenerative diseases.