Risk of dementia in an elderly population of Parkinson's disease patients: a 15-year population-based study.

Background: The incidence of dementia in Parkinson's disease (PD) is not fully known, and previous studies have provided a wide range of rates owing to variations in diagnostic criteria and methodologies used. We estimated the risk of dementia in newly diagnosed cases of PD in a population-based cohort of subjects aged >65 years.

Methods: We performed repetitive systematic screening of PD diagnosis, cognitive performances, and clinical dementia during 15 years (at year 0, 3, 5, 8, 10, and 15) in 3726 elderly subjects living at home in southwestern France (PAQUID). Two sets of diagnostic criteria for dementia in PD were considered: Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised criteria and Movement Disorders Society criteria.

Results: Forty-four incident cases of PD occurred in the cohort; of these, 18 (41%) developed dementia during a mean follow-up of 6.8 ± 3.6 years. Incidence rate of dementia associated with PD was 74 per 1000 patient-years. The cumulative risk of dementia was approximately 25% and 50% after 5 and 10 years of follow-up, respectively. The relative risk for developing dementia in incident PD subjects compared with non-PD subjects was 2.47 (1.55-3.95). Equivalent estimations were obtained with Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised criteria or Movement Disorders Society criteria.

Conclusion: PD represents a high-risk stage for dementia in the general population.