Environmental risk factors for amyotrophic lateral sclerosis: a case-control study in Canada and France.

Objective

To evaluate the association between amyotrophic lateral sclerosis (ALS) and potential environmental risk factors, especially head traumas and pesticides, in two populations from Canada and France.

Methods

A case-control study was performed in tertiary-care centers. Consecutive ALS cases were recruited along with a control group from the same age distribution and region. Participants answered a phone-administered questionnaire. Head trauma exposure was censored at age of symptom onset, and a sensitivity analysis considering old head traumas that occurred more than 3 years before onset was performed. Univariate and multivariate logistic regression were used to estimate odds ratios (ORs) and their 95% confidence intervals (CIs).

Results

A total of 404 ALS cases and 381 controls completed the questionnaire. Previous head trauma was more frequently reported by cases (adjusted OR 1.50 (1.05-2.18)) with a dose-response relationship. This association was driven by a strong effect in men (adjusted OR 2.06 (1.22-3.55)) and was consistent for old traumas, but there was no association in women. For pesticides, a previous high-risk occupation was associated with ALS (adjusted OR 2.08 (1.36-3.24)), although reported occupational exposure to pesticides was not statistically significant in the multivariate model (adjusted OR 1.67 (0.97-2.97)). Past electrocution was associated with ALS (adjusted OR 1.79 (CI 1.13-2.87)), especially spinal-onset ALS. Residential exposure to pesticides, neck trauma, and welding were not associated with ALS.

Conclusions

Head trauma is a risk factor for ALS in men only. Previous occupation at high risk for pesticides exposure and electrocution are also risk factors for ALS.