Introduction

Excessive daytime sleepiness (EDS) can be a feature of various neurodegenerative diseases including Parkinson's disease (PD). EDS puts patients at increased risk of accidents while driving and it is important to identify such patients in order to advise them and others about their individual level of risk and the potential therapeutic options available to them.

The most commonly used method for assessing EDS in the clinic is the Epworth Sleepiness Scale (ESS)—a self-completed questionnaire which scores the tendency to fall asleep during eight everyday situations. The final score ranges from 0–24, with scores greater than 10 generally considered pathological. This questionnaire has been widely used in unselected PD cohorts, with the prevalence of EDS ranging from 3–50%.1 Although there is a general consensus that dopaminergic medications contribute to EDS in PD,2 there is less agreement about other risk factors. One possible explanation for these disparities is that heterogeneous PD cohorts were studied at different points in their disease course. Some studies have also suggested that the Catechol O-methyltransferase (COMT) val¹⁵⁸met polymorphism (which is known to significantly alter enzyme activity) may be associated with EDS.

In this study, we report on the prevalence of EDS and its risk factors in a population-representative incident PD cohort.