A longitudinal of Parkinson's disease: clinical and neuropsychological correlates of dementia.

Neuropsychological assessments were performed in ninety-one de novo patients participating in the Sydney Multicentre Study of Parkinson's disease. Assessments were made at baseline and after 3 and 5 years. Performance at baseline and after 5 years was compared with controls. At baseline 37% of patients whose symptoms of Parkinson's disease had begun after the age of 70 years were demented. This compared with a prevalence of dementia of 8.8% in patients whose symptoms had begun before the age of 70 years. By 5 years the prevalence of dementia in the two groups had risen to 62.3% and 17.3% respectively. The death rate was higher over the 5 year period in the demented patients. Demented patients had more symmetrical signs, higher disability and bradykinesia scores and more impairment of gait and balance at baseline than non-demented patients. The presence of dementia at baseline predicted a poor response to treatment. The dementia at baseline had features of a subcortical dementia. Subsequently, aphasia, apraxia and agnosia emerged, making the dementia indistinguishable from that of Alzheimer's disease. Patients with well preserved cognitive function at baseline had a good response to levodopa and were more likely to develop levodopa induced dyskinesia. These results show that the clinical features of Parkinson's disease and response to treatment are influenced by the age of onset of symptoms and by the presence of dementia.