Background: Most prognostic studies on Parkinson disease have been hospital based or have applied register-based case-finding methods. Potential under-representation of mild cases may have given biased results.
Objective: To evaluate whether Parkinson disease is associated with an increased risk of dementia and death.
Design: Population-based cohort study. Parkinson disease and dementia were assessed through in-person examination at baseline (1990-1993) and 2 follow-up visits (1993-1994 and 1997-1999). Computerized linkage to medical and municipality records provided additional information on disease outcomes and mortality.
Setting: General population.
Participants: A total of 6969 participants, including 99 prevalent and 67 incident cases of Parkinson disease.
Main outcome measures: Incident dementia and death. Adjusted hazard ratios were calculated through Cox proportional hazards regression analysis.
Results: Patients with Parkinson disease had an increased risk of dementia (hazard ratio, 2.8; 95% confidence interval, 1.8-4.4), which was especially pronounced in participants carrying at least 1 apolipoprotein E gene (APOE) epsilon2 allele (13.5; 4.5-40.6). Parkinson disease was associated with an increased mortality risk (1.8; 1.5-2.3). The association consistently diminished when analyses were sequentially restricted to patients with shorter disease duration and after adjustment for the occurrence of dementia.
Conclusions: Especially patients with Parkinson disease who carry an APOE epsilon2 allele have an increased risk of developing dementia. Increased mortality risk in Parkinson disease is dependent on disease duration and is only modest in the absence of dementia.