Association of lead exposure with survival in amyotrophic lateral sclerosis

BACKGROUND: Reasons for the variability in survival among ALS cases are unknown but may include exposure to environmental neurotoxicants. OBJECTIVES: We aimed to determine whether lead exposure, assessed by measuring blood and bone lead levels, is associated with survival in amyotrophic lateral sclerosis (ALS). METHODS: We evaluated the relationship of lead exposure to ALS survival in 110 cases from a case-control study conducted in New England in 1993-1996 that included measurements of blood and bone lead. We retrieved information on date and cause of death through 31 December 2003 from the National Death Index Plus and the Social Security Administration Death Index. We evaluated the relationship of survival to lead exposure using Cox proportional hazard analysis, with adjustment for age, sex, and smoking. RESULTS: We found mortality data for 100 of 110 cases; 93 of 100 death certificates mentioned ALS. Median survival from diagnosis to death was 28 months. Shorter survival was associated with older age at diagnosis, female sex, bulbar onset, shorter interval between symptom onset and diagnosis, and reduced lung function. Shorter survival from diagnosis to death had a weak inverse association with blood lead (hazard ratio = 0.9; 95% confidence interval, 0.8-1.0) and a stronger inverse association with patella lead (0.5; 0.2-1.0) and tibia lead (0.3; 0.1-0.7); similar results were found for survival from symptom onset to death. CONCLUSIONS: These results suggest that lead exposure is associated with longer survival in ALS cases and, if confirmed, may shed light on mechanisms involved in disease progression.