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Neurology 2000 Apr 25;54(8):1596-603 A 10-year study of the incidence of and factors predicting dementia in Parkinson's disease. Hughes TA, Ross HF, Musa S, Bhattacherjee S, Nathan RN, Mindham RH, Spokes EG Division of Psychiatry and Behavioural Sciences (T.A. Hughes, H.F. Ross, S. Musa, S. Bhattacherjee, R.N. Nathan, and R.H.S. Mindham), University of Leeds, and the General Infirmary at Leeds (E.G.S. Spokes), UK. OBJECTIVE: To compare the incidence of dementia in PD with that of a control group without PD, and to assess the relationship between dementia and other features of PD. METHODS: The authors recruited 83 patients with PD and 50 controls, all without dementia at initial assessment, and assessed them at regular intervals over a maximum period of 122 months. Dementia was diagnosed according to objective criteria, and included a judgment by researchers masked to subject group and to variables putatively associated with dementia. RESULTS: Seventeen patients fulfilled dementia criteria; no controls did so. The cumulative proportion of PD patients becoming demented by 112 months was 0.38 (95% CI 0.20 to 0.55), or 42.6 cases per 1000 years of observation. Univariate analyses showed that incident dementia in patients with PD was associated with older age at entry into the study, greater severity of neurologic symptoms, longer duration of PD, greater disability, and male sex. The association of age at onset of PD with incident dementia was of only borderline significance. Multivariate analysis found that age at entry into the study and severity of motor symptoms were significant predictors of dementia but duration of PD and age at onset of PD were not. CONCLUSIONS: Dementia in PD is likely to reflect interaction of the neuropathology of the basal ganglia and age-related pathology. The findings do not support the division of PD into early and late-onset cases.