Sleep Disturbance in Parkinson's Disease: Consequences for the Brain and Disease Progression - A Narrative Review.

Sleep disturbance in Parkinson's disease (PD) is recognized to be one of the most common non-motor complications. It occurs before disease onset as a prodromal symptom, during and then throughout the disease course. Causes are multifactorial and can be multiple in the same patient. Specific sleep disorders that are known to occur in those with Parkinson's disease include REM sleep behavior disorder, sleep disordered breathing including obstructive sleep apnea, restless legs and periodic limb movements, nightmare disorder, insomnia alongside direct side-effects of the medication used for therapy. One key question is whether these sleep disorders impact upon the motor and non-motor symptoms of Parkinson's disease. There has been significant interest in recent years in using certain sleep disorders, in particular, REM sleep behavior disorder, as a biomarker both for those at risk of Parkinson's disease but also influencing the subsequent severity and speed of progression. However, other sleep disorders in the general population may also increase the risk of developing Parkinson's disease. It is important to understand whether the treatment of sleep disturbance and specific sleep disorders modifies the long-term risk of developing Parkinson's disease or its progression.