Electroencephalographic Finding in Idiopathic REM Sleep Behavior Disorder.

The REM sleep behavior disorder (RBD) is a type of parasomnia manifested by vivid, often frightening dreams associated with motor behaviors during REM sleep, sometimes causing injuries to patients themselves or to their bed partners. The polysomnographic features of RBD include increased muscle activity during REM sleep (REM sleep without atonia). The majority of RBD-affected persons are older men. The disorder might be idiopathic (iRBD) or secondary to neurological disorders of various kinds. iRBD management with pharmaceutical measures is usually straightforward and effective. Several longitudinal studies have revealed that a high proportion of iRBD patients convert to α-synucleinopathies such as Parkinson's disease and dementia with Lewy body disease (DLB). Considering this, many studies have been conducted to identify common clinical markers between α-synucleinopathies and iRBD or indicators for the future development of α-synucleinopathies in iRBD patients. In this context, electroencephalographic (EEG) slowing occurring while awake and asleep, which is frequently observed in DLB, has received much attention. Clarification of the association between EEG slowing and the presence of mild cognitive impairment, which is also commonly seen in early stages of DLB, has been particularly expected to offer a breakthrough for the identification of cases which might convert to α-synucleinopathies. In this article, we introduce the progress in quantitative EEG research in iRBD during the past decade. We also discuss the relationship between EEG findings and cognitive decline as well as the mechanisms of EEG changes or cognitive abnormalities in patients with the disorder.