Depression as a Potential Moderator of the Sleep-Apathy Association in Parkinson's disease: Exploratory Evidence from...

Parkinson's Disease (PD) involves a complex interplay of non-motor symptoms-sleep disturbances, depression, and apathy-that significantly impair quality of life. However, the moderating role of depression in the sleep-apathy relationship remains poorly understood.

This study explored the potential moderating role of depressive symptoms in the link between sleep disturbances and apathy in patients with PD.

Two independent cross-sectional studies were conducted (Study 1: 197 PD, 394 controls; Study 2: 100 PD, 178 controls). Sleep quality was assessed via the Pittsburgh Sleep Quality Index. Depression and apathy were measured using the Neuropsychiatric Inventory (Study 1) and the Geriatric Depression/Apathy Scales (Study 2). Moderation analyses were performed across cohorts.

Depressive symptoms were associated with moderation patterns in the association between sleep disturbance and apathy in PD patients, but not in controls. Specifically, sleep latency tended to interact with depressive symptomsin ralation to apathy severity (Study 1), and in Study 2, this suggested interaction was particularly evident for "dropped activities/interests," which was linked to cognitive apathy. While these exploratory patterns showed directional consistency, they did not remain robust after formal mutiple comparison correction and full adjustment for confounders (including anxiety, fatigue, pain, and motor severity).

Depressive symptoms suggest a potential and preliminary exploratory interaction between sleep disturbance and apathy in PD, which warrants cautious interpretation given its attenuation after adjusting for broader symptom burden. These preliminary findings highlight the value of further investigating integrated, symptom-focused management strategies that address co-occurring non-motor symptoms in PD.