Objective: To investigate whether patients with a diagnosis of affective disorder are at an increased risk of developing Parkinson's disease compared with medically ill control groups.
Method: By linkage of public hospital registers from 1977 to 1993, three study cohorts were identified: patients with affective disorder episodes (mania or depression) and patients with osteoarthritis or diabetes. Time to the first diagnosis of Parkinson's disease was estimated with the use of survival analysis.
Results: A total of 164 385 patients entered the study base. The risk of being given a diagnosis of Parkinson's disease was significantly increased for patients with affective disorder, odds ratio 2.2 (CI 95% 1.7-2.8) compared with osteoarthritis, and depressive disorders, odds ratio 2.2 (CI 95% 1.7-2.9) compared with osteoarthritis.
Conclusion: This study supports the hypothesis of a common aetiology for major affective disorder and Parkinson's disease.