Parkinsonian signs in older people in a community-based study: risk of incident dementia.

BACKGROUND: Mild parkinsonian signs occur in 30% to 40% of community-dwelling older people. In a cross-sectional study, the severity of these signs was greater in people with dementia than in people without dementia.
OBJECTIVE: To determine whether baseline mild parkinsonian signs are a predictor of incident dementia.
DESIGN: A prospective, longitudinal study of community-dwelling older people who did not have dementia or Parkinson disease at baseline.
METHODS: A neurological examination was performed on 1028 residents aged 65 years or older in the Washington Height-Inwood community in northern Manhattan, NY. Parkinsonian signs were rated with an abbreviated Unified Parkinson's Disease Rating Scale, resulting in a parkinsonian sign score (range, 0-40). The risk of incident dementia was assessed using Cox proportional hazards models. In some analyses, data from the modified Unified Parkinson's Disease Rating Scale were divided into 3 domains: rigidity, axial function, and tremor at rest.
RESULTS: The mean duration of follow-up was 5.6 years, and 224 participants (21.8%) developed dementia. In a Cox model, the risk of incident dementia was 57% higher in participants with a baseline parkinsonian sign score of 2 vs 0 (relative risk, 1.56; 95% confidence interval, 1.04-2.33; P =.03). In a second Cox model, the baseline parkinsonian sign score was associated with incident dementia (relative risk, 1.08; 95% confidence interval, 1.01-1.16; P =.02) independent of associations with baseline age, education, ethnicity, diabetes mellitus, and stroke.
CONCLUSIONS: Baseline mild parkinsonian signs are a predictor of incident dementia. Although these signs are mild, they are not prognostically benign. Brain imaging and postmortem examinations might further our insight into the anatomical and pathological basis for mild parkinsonian signs.