Time trends in the incidence of parkinsonism in Olmsted County, Minnesota

Objective: To investigate time trends in the incidence of parkinsonism and PD over a 15-year period (1976 to 1990). Methods: The authors used the medi cal records-linkage system of the Rochester Epidemiology Project to identif y incidence cases of parkinsonism in Olmsted County, MN, over three 5-year periods, 1976 to 1980, 1981 to 1985, and 1986 to 1990. PD and other types o f parkinsonism were classified using defined criteria. Population denominat ors were derived from census data and were corrected by removing prevalent cases of parkinsonism. Results: Over the 15 years of the study, 364 cases o f parkinsonism were identified; 154 (42%) of them had PD. The incidence of parkinsonism remained stable over the three 5-year periods for the age clas ses 0 to 39, 40 to 59, and 60 to 69 years. For the age class 70 to 99 years , there was some increase over time mainly owing to an increased incidence of drug-induced parkinsonism. The incidence of PD remained stable over the three 5-year periods for all age classes. Results were similar when conside ring men and women separately. No birth-cohort effect was present for parki nsonism. Comparison with three previous studies in the same population did not reveal any major long-term secular trends in the incidence of parkinson ism. Conclusions: The findings for PD over 15 years and comparison of the f indings with historical data for parkinsonism over half a century suggest t hat no major environmental risk factors for PD (e.g., environmental toxins, drugs, diet constituents, or infectious agents) were introduced or removed from this population during these periods.