Contributions of dopaminergic drugs and disease severity to daytime sleepiness in Parkinson disease

Background: Excessive daytime somnolence is a common report among patients who have Parkinson disease (PD). The relative contributions of disease severity and of the various dopaminergic drugs are unclear. Objective: To separate and quantify the contributions of disease markers and drug doses. Methods: Patients seen during a 7-month period at a center for movement disorders completed the Epworth Sleepiness Scale. Treatment subgroups were compared. The relationship to sedation of age; dopaminergic drug classes and doses; Hoehn and Yahr stage; duration of disease; total score on the motor subsection of the Unified Parkinson Disease Rating Scale; and the presence or absence of dementia, depression, or hallucinations was calculated using simple and multiple regression and t tests. Results: The Epworth Sleepiness Scale scores were higher among patients with PD (mean [SD], 10.8 [5.3]; n = 368) compared with patients with other neurological disorders (mean, 8.5 [5.1]; n=243; P<.001). A model containing the Hoehn and Yahr stage, levodopa dose, and use of a dopamine agonist was the best at predicting the total score of Epworth Sleepiness Scale in patients who have PD, but accounted for only 9% of the interindividual variance. The parameter estimates (SE) corresponded to a 1.02 (0.03)-point increase per Hoehn and Yahr stage, a 0.14 (0.06)-point increase per 100-mg increase in levodopa dose over 24 hours, and a 2.33 (0.57) point increase with use of an agonist. There was no statistically significant dose response for agonists. No statistically significant difference in sedation among the commonly used dopamine agonists was found. Conclusions: Somnolence in patients with PD, which is on average 25% higher than in other neurological diseases, is related to PD stage, levodopa dose, and the use of a dopamine agonist. However, most of the variability in sedation levels in patients with PD as well as in controls is the result of, as yet, unidentified factors.