Prodromal Markers in Recurrent Dream Enactment Behaviors Without REM Sleep Without Atonia

REM sleep behavior disorder is a novel and distinct parasomnia characterized by recurrent dream enactment behaviors (DEBs) and REM sleep without atonia (RSWA) during polysomnographic assessment, with a male predominance and typical onset age at early 60's. The majority of patients with idiopathic RBD (iRBD) will eventually develop α-synucleinopathy, for instance Parkinson's disease (PD). Thus, iRBD has been considered as a highly specific precursor of α-synucleinopathy-related neurodegeneration. Recently, increasing studies have found that some participants present with only RSWA or DEBs (but without sufficient RSWA), which does not meet the diagnostic criteria for RBD. It has been suggested that these participants with subclinical features (either DEBs or RSWA) might represent a condition known as prodromal RBD. Several emerging evidence, including our own study, have implied a link between isolated RSWA (RSWA without DEBs) and markers of α-synucleinopathy-related neurodegeneration. However, it is still unclear whether the other condition related to RBD, i.e. recurrent DEBs but without sufficient RSWA, is related to a certain degree of α-synucleinopathy. In this regard, the novel concept of recurrent DEBs but without sufficient RSWA, also termed as prodromal/isolated RBD by some researchers, requires validation by further evidence in terms of clinical feature and neurodegenerative prodromal markers perspectives.