The effect of age of disease onset on neuropsychological performance in Parkinson's disease.
One hundred and eight noninstitutionalized patients with Parkinson's disease were studied to find out whether the age of disease onset affects patients' cognitive, memory and psychomotor performance. "Early onset" patients (whose disease began before 60 years of age) showed a wide spectrum of impairments in neuropsychological performance compared with age-matched normal subjects. However, only one (2%) of these patients was demented according to DSM III criteria. Dementia was more frequent in patients with equivalent disease duration, but with late onset of disease (over 60 years); 13 of such patients (25%) were demented. The present study supports previous findings which show that dementia increases with advancing age in Parkinson's disease. It also suggests that cognitive changes are also found in patients with early onset of disease.