Excessive daytime somnolence in Japanese patients with Parkinson's disease.

To investigate the prevalence and severity of excessive daytime somnolence (EDS) in Japanese patients with Parkinson's disease (PD) and to examine the main cause of EDS. Fifty-three Japanese patients with PD (PDs: 32 females and 21 males) and 17 controls (10 females and seven males) were evaluated using the Epworth Sleepiness Scale (ESS). The severity of the disease was evaluated by Unified Parkinson's disease Rating Scale (UPDRS), and information about quality and quantity of medications was collected. The correlations amongst EDS and age, severity of PD, duration of illness and medications were analyzed. The mean ESS score was significantly higher in advanced PDs than in controls, and correlated with the UPDRS score (r(s) = 0.743, P < 0.0001). Age, duration of illness and the dose of levodopa weakly correlated with ESS score. The intake of dopamine agonists did not affect the severity of EDS. The mean ESS score in PDs was lower than that reported in PD in European and American studies. EDS in Japanese patients with PD was milder compared with Caucasian patients, which might be due to the lower doses of the medications used in Japan. The results suggest that EDS in PD is mainly because of neuropathological changes of the disease itself.