La lévodopa est-elle néfaste pour la cognition dans la maladie de Parkinson? : étude pilote
Background and objectives: While levodopa’s effect on motor symptoms in Parkinson’s disease (PD) has been largely characterized, its cognitive effect still remains without definite conclusion. Since cognitive impairment is an important feature of PD that impacts patients’ quality of life, it is important to establish levodopa’s effect on cognitive functions. Multiple studies regarding this subject remained without specific consensus. The main goal pursued in this study is to observe the effect of clinical doses of levodopa on attention and executive functions. A dose-response curve is also made with the escalating doses evaluated. Methods: Five PD patients were investigated OFF (minimal withdrawal of 12 hours) and ON levodopa (starting dose of 50mg escalating by 50mg per visit) with 2 cognitive (CPT-II and Stroop) and 2 motor (finger tapping and UPDRS-III) tests until reaching an optimal cognitive performance or showing signs of side effects. Practice sessions of the cognitive tests were done at the first visit. Results: While reaction time (RT) in milliseconds increased (median 3.03%), errors slightly decreased (median -9.92%) after medication intake in the CPT-II. Errors however did not change in the Stroop while time evaluated in seconds decreased. The CPT-II showed slowing at the prescribed doses of levodopa (3.5%) while lower doses improved errors with less increase of the RT. These small doses also improved the performance in the Stroop test with a 19% reduction in time while the prescribed doses improved errors instead. The dose-response curve indicates a reduction of errors in the CPT-II for low and high doses while time usually increased, showing a more cautious style. Besides the beneficial effect of low doses, the dose-response curve for the Stroop test did not show any specific tendencies in levodopa’s effect on interference. An important variability was observed in motor evaluations between and within subjects. Conclusion: These results indicate that levodopa does not seem to have an important deleterious effect on attention and executive functions evaluated in this group of parkinsonian patients and that low doses seem to even be beneficial and better than the ones usually taken by the patients. The dose-response curve showed that the cognitive effect of levodopa for these patients varies between the different doses without being clear on the tendencies.
Attention Parkinson disease Cognitive impairment Executive functions Escalating doses Dose-response