Objective: Sleep-wake disturbances, such as excessive daytime somnolence (EDS), are nonmotor symptoms of Parkinson's disease (PD) and significantly affect the quality of life. This study aimed to examine the relationship between EDS and motor and nonmotor symptoms of PD.
Methods: Eighty-two patients with idiopathic mild PD were followed up twice a year for 2 years and assessed on sleep, mood, anxiety, cognition, function, and disease severity. Data were analyzed retrospectively, comparing motor and nonmotor outcomes between those with EDS and those without.
Results: At baseline, 27.9% had EDS and were similar in demographic and clinical characteristics to those without; 10% had persistent EDS during the first year of follow-up. Excessive daytime somnolence had a significant main effect on mood and anxiety as shown by consistently higher scores on the Geriatric Depression Scale (P = .022) and Hospital Anxiety and Depression Scale-Anxiety subscale scores (P = .011) throughout duration of follow-up. The group with persistent EDS showed greater rate of worsening Frontal Assessment Battery scores by the end of first-year follow-up (P = .025) and greater rate of worsening Apathy Scale scores by the end of 2-year follow-up (P = .002). No significant effects of EDS on motor symptoms and disease severity were found.
Conclusions: In a Southeast Asian cohort of patients with PD, EDS had a negative longitudinal impact on mood, anxiety, apathy, and cognitive function but no impact on motor symptoms and disease severity. Excessive daytime somnolence is thus a potential therapeutic target to improve nonmotor outcomes.
Keywords: Parkinson's disease; anxiety; cognitive impairment; depression; movement disorder; neurodegeneration.