Can levodopa prevent cognitive decline in patients with Parkinson's disease?

Abstract

Cognitive impairment in Parkinson's disease (PD) will become more important since the number of elderly patients with PD is increasing. We prospectively studied non-demented patients with PD over the course of 3 years to identify factors associated with PD that contribute to a decline in cognitive function. From among 100 consecutive patients, we registered 79 patients with PD. A total of 55 patients completed the study during 3 years and were divided to two groups: patients with a decline in cognitive function and those without a decline in cognitive function after 3 years. Seventeen independent variables were evaluated with the use of logistic regression models. The increase in the daily levodopa dose was related to a decline in cognitive function on univariate logistic regression analysis (OR = 0.279, p = 0.024, 95% CI = 0.092-0.848). Other variables were not related to a decline in cognitive function. The increase in the daily dose of levodopa was greater in patients without a decline in cognitive function than those with a decline in cognitive function; on the other hand, the cognitive function unchanged. Our results suggest that the treatment with levodopa might prevent a decline in cognitive function in PD.

Keywords: Parkinson; cognition; dementia; dopamine; levodopa.

Figure 1

Selection procedure for patients included in analysis. From among the 100 patients, we excluded 11 patients who did not complete the required initial examinations during the first 4 weeks and 10 patients who had an MMSE score of < 24. We registered 79 patients and could finally follow up 57 patients for 3 years. In addition, we excluded two patients who could not continue our examinations after 3 years. The remaining 55 patients were included in data analysis.

Figure 2

Daily levodopa dosage or Mini-Mental Status Examination (MMSE) between patients with a decline in cognitive function and those without a decline in cognitive function after 3 years. In patients with a decline in cognitive function at the study entry, the score for MMSE was decreased. On the other hand, the cognitive function unchanged in patients without a decline in cognitive function at the study entry. The increase in the daily dose of levodopa was greater in patients without a decline in cognitive function than those with a decline in cognitive function.