Incident and prevalent ALS patients were recruited in Quebec and France along with a control group composed of relatives of ALS and Parkinson patients and patients from neurology clinics not suffering from neurodegenerative disorders. Exposition was evaluated by a phone-administered questionnaire in which patients were asked whether they had occupied a list of at-risk jobs, and then whether they had actually used pesticides in this occupational setting. Results were analysed with unadjusted and adjusted unconditional logistic regression taking as covariates age, gender, cigarette smoking, and head trauma history.

403 cases and 381 controls were included. Mean age at questionnaire was 59.2 years (±11.8 years) in cases and 58.8 years (±11.1 years) in controls, and 85 cases (21.1%) presented with bulbar onset. At-risk occupation was reported in 85 cases (21.1%) and 37 controls (9.7%), which yielded an unadjusted OR of 2.48 (95%CI 1.65-3.80; p<0.0001), and an adjusted OR of 2.00 (95%CI 1.31-3.11; p=0.002) when controlling for age, gender, smoking, and head trauma. Actual occupational exposition to pesticides was reported in 45 cases (11.2%) and 22 controls (5.8%), for an unadjusted OR of 2.05 (95%CI 1.22-3.54; p=0.008) and an adjusted OR of 1.53 (95%CI 0.89-2.69; p=0.13). There was no statistical interaction between gender, head trauma and at-risk occupation or actual pesticide occupational exposition.

Our results show an association between occupations at high risk for pesticides exposition and ALS, but this association was not statistically significant when we considered only actual exposition to pesticides in these occupational settings in a multivariate analysis.