Dementia and treatment with L-dopa in Parkinson's disease.

We compared the neuropsychological performance of patients with Parkinson's disease who were young at onset of the disease (mean age, 41.4 years) and had received prolonged L-dopa treatment (mean, 52.1 months) with nontreated patients of the same age. A similar comparison was made for patients who were older at onset of the disease (mean, 62.1 years). There were no significant differences in cognitive and memory functions between the L-Dopa-treated and untreated young patients, whereas the L-Dopa-treated patients in the older age group performed more poorly than untreated patients in some memory tests (Wechsler Memory Scale I: logical and visual) and cognitive functions (Wechsler Adult Intelligence Scale: similarities, block design, and cognitive flexibility). Treatment duration, disease duration, and mean L-Dopa dose were comparable for the two age groups. After linear effects of age and disease duration had been eliminated, the duration of L-Dopa treatment did not correlate with the cognitive variables studied. These observations suggest that treatment with L-Dopa may not be the cause of cognitive impairment in Parkinson's disease.