ObjectiveRapid eye movement (REM) sleep behavior disorder (RBD) is commonly associated with Lewy body disease, narcolepsy, or depression. In contrast, the relationship between REM sleep without atonia (RWA), which is a hallmark of RBD on polysomnography, and clinical characteristics remains unclear. The purpose of this study is to investigate the clinical features of psychiatric patients exhibiting RWA and its relevance to Lewy body disease. MethodsOf 55 consecutive patients who underwent polysomnography at the psychiatric ward, 25 patients with sleep apnea syndrome were excluded, and 12 patients exhibiting RWA were identified. The clinical profiles were compared between the groups with and without RWA. ResultsThe mean age and the frequency of neurocognitive disorders were significantly higher in 12 patients with RWA than in 18 without. Only five of the 12 patients exhibiting RWA had episodes of dream-enactment behavior, and fulfilled the clinical criteria for RBD. Two young patients were diagnosed with narcolepsy, while the other middle-aged and older patients fulfilled the clinical criteria for Parkinson's disease (n=1), dementia with Lewy bodies (n=4), idiopathic RBD (n=2), and major depressive disorder (MDD) (n=3). The patients with MDD exhibited constipation and/or olfactory dysfunction. Moreover, neuroimaging examinations in the patients with MDD revealed isolated occipital hypoperfusion in three patients and mild dopamine transporter deficit in one patient. ConclusionsRapid eye movement sleep without atonia itself may be associated with specific clinical profiles, even when dream-enactment behavior is absent. Continued follow-up of the patients with MDD exhibiting RWA is warranted to determine if they represent the prodromal Parkinson's disease/dementia with Lewy bodies. Copyright (c) 2016 John Wiley & Sons, Ltd.