"Sleep benefit" in Parkinson's disease: a systematic review.

Sleep disorders are common among patients with Parkinson's disease (PD). However, there are also reports of PD patients experiencing a beneficial effect of sleep. Upon awaking in the morning some patients experience good mobility, as if they are in an "on" state induced by medication, contrary to what would be expected after a night without medication. This intriguing phenomenon is known as sleep benefit. Here, we review the available research on sleep benefit in PD, describing its prevalence, clinical effects and determinants. We also discuss the possible mechanisms underlying sleep benefit, and the potential clinical applicability. Finally, we propose a new definition of sleep benefit to allow for improved standardization and homogeneity in future research. Important research targets include the development of objective measures of sleep benefit, as a basis for obtaining a better understanding of sleep benefit, its underlying mechanisms and its potential therapeutic application.