Chronic effects of dopaminergic replacement on cognitive function in Parkinson's disease:: A two-year follow-up study of previously untreated patients

BACKGROUND: The cognitive effects of dopaminergic treatment in Parkinson's disease (PD) are still controversial. OBJECTIVE: To evaluate, in previously untreated patients with PD, whether chronic dopaminergic stimulation produces significant cognitive changes; whether they are sustained beyond the period of a few months; and whether the cognitive status of two motor-comparable groups is differently affected by levodopa and pergolide. DESIGN AND SUBJECTS: Parallel, randomized open study with blind neuropsychologic evaluation of 20 consecutive de novo patients with PD before and 3, 6, 12, 18, and 24 months after monotherapy with levodopa (n = 10) or pergolide (n = 10; 6-month monotherapy; pergolide + levodopa thereafter). RESULTS: Both treatments were associated with a significant improvement in motor scores and in tests assessing learning and long-term verbal and visual memory, visuospatial abilities, and various frontal tasks. While improvement in motor scores persisted, improvement in activities of daily living and in semantic fluency, Luria's rhythm and motor and long-term memory tests was not sustained at the 24-month examination. Further, performance on attentional, short-term memory, and the Stroop tests did not change over the course of the study. CONCLUSIONS: Both treatments were associated with incomplete but long-lasting (18 mos) improvement in many cognitive tasks which declined thereafter, suggesting that dopaminergic replacement is not enough to compensate for all cognitive deficits of PD.