Abstract
BACKGROUND: Non-motor complications of Parkinson's disease (PD), specifically cognitive impairment, sleep disturbances, and fatigue, are recognized as important contributors to poor patient outcomes and quality of life. How sleep problems and fatigue interrelate and impact cognitive function, however, has not systematically been investigated across the stages of PD. The aim of our study was to investigate the relationships among cognitive impairment, night-time sleep problems, daytime sleepiness, and fatigue across all severities of PD. METHODS: We examined these non-motor problems using the Movement Disorder Society-Sponsored Revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) in a study of 1319 PD patients drawn from three large cohort studies: the Parkinson's Progressive Markers Initiative, the Rush University PD Cognitive-Behavioral-Imaging study, and the Movement Disorder Society-Unified Parkinson's Disease Rating Scale Clinimetric testing program study, which spanned the gamut of disease, from early to advanced PD. Generalized linear mixed models with logit linking functions and covariates including study cohort, age, PD duration, and presence/absence of PD medications were used to examine relationships between these three non-motor symptoms and cognitive impairment. RESULTS: Of these three frequent, and often inter-twined, non-motor complications, greater daytime sleepiness and fatigue were associated with worse cognitive impairment across the full spectrum of PD (F[16,1158] = 2.40 and F[16,1158] = 3.45 respectively, p's < 0.0005), but an association with night-time sleep was not detected (p = 0.83). CONCLUSIONS: Given this association of daytime sleepiness and fatigue with cognitive impairment, clinical monitoring for these problems should be considered across all points in the PD spectrum, from early to more advanced disease.