Neuropsychological functioning in Parkinson's disease: Differential relationships with self-reported sleep-wake disturbances

Background: Sleep disturbance may represent a risk factor for the development of dementia in Parkinson's disease. However, prior studies exploring the association between specific sleep-wake disturbances and neuropsychological functions have been limited. Methods: In this study, 101 patients with idiopathic Parkinson's disease were assessed neurologically, underwent neuropsychological testing, and completed self-report questionnaires covering nocturnal disturbance, excessive daytime sleepiness, and symptoms of rapid eye movement sleep behavior disorder. Results: Univariate correlations revealed differential patterns of neuropsychological performance in relation to nocturnal sleep disturbance, excessive daytime sleepiness, and rapid eye movement sleep behavior disorder. After controlling for potential confounders, excessive daytime sleepiness remained a significant predictor of slowed processing speed, and rapid eye movement sleep behavior disorder predicted working memory and verbal fluency performance. The relationships between nocturnal sleep disturbance and memory appeared to be mediated by education. Conclusions: These findings highlight the critical role that specific sleep-wake disturbances in Parkinson's disease might have on neuropsychological functioning, which may reflect common neural underpinnings.