Drug-induced parkinsonism as a risk factor for Parkinson's disease: A historical cohort study in Olmsted County, Minnesota

Objective: To investigate whether subjects who experienced a reversible episode of drug-induced parkinsonism have an increased risk of subsequent Parkinson's disease. Design: We undertook a historical cohort study based on the medical records-linkage system of the Rochester Epidemiology Project in Olmsted County, Minnesota. Material and Methods: All subjects in whom drug- induced parkinsonism developed between 1955 and 1990 and was indexed in the medical records-linkage system were identified. In the 24 eligible subjects, follow-up for the subsequent development of Parkinson's disease conSisted of a total of 192.7 person-years. The observed number of cases of Parkinson's disease was compared with the expected number of cases in an age- and sex- matched cohort from the general population. Results: In 2 of 24 subjects with drug-induced parkinsonism, Parkinson's disease later developed. A comparison with the expected number of cases in the general population (0.08) yielded a relative risk of 24.3 (95% confidence interval, 2.9 to 87.5; P = 0.006). Conclusion: Our findings suggest that drug-induced parkinsonism is associated with an increased risk of Parkinson's disease. Clarification of the mechanisms of this association may have preventive implications.