**1. Introduction**

180 Sleep Disorders

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> REM sleep behavior disorder (RBD) is a parasomnia characterized by dream-enacting behavior and vivid, action-filled or unpleasant dreams and presents a risk for self-injury and harm to others (e.g., a bed partner) due to abnormal REM sleep during which control of muscle tonus is lacking. Polysomnography is required to establish the diagnosis and represents the diagnostic gold standard for revealing loss of REM-related muscle atonia with excessive sustained or intermittent elevation of submental EMG tone or excessive phasic submental or limb EMG twitching. Idiopathic RBD (iRBD) has a male preponderance and usually emerges after the age of 50 and has a known association with neurodegenerative diseases, in particular the α-synucleinopathies such as Parkinson's disease (PD), dementia with Lewy body disease and multiple system atrophy (Schenck & Mahowald, 2002). Even more important, evidence is growing that iRBD precedes parkinsonism by years or even decades, and that iRBD might present an early stage in the development of neurodegenerative disorders (Schenck et al., 1996). Thus, to identify clinical RBD as early as possible appears to be useful for early diagnosis, a clinical trial with a potentially neuroprotective substance, and also for epidemiological studies. To meet the need for an easily applicable diagnostic screening tool, Stiasny-Kolster et al. developed and validated a specific screening scale for assessment of RBD, the RBD screening questionnaire (RBDSQ) (Stiasny-Kolster et al., 2007). Subsequently we developed a Japanese version of the RBDSQ (RBDSQ-J) after obtaining approval from the patent owner and investigated its validity and reliability (Miyamoto et al., 2009). We found that detection of RBD using the RBDSQ-J would be useful in the stepwise diagnostic process. We will discuss screening methods for RBD and describe RBD screening questionnaires, including the RBDSQ-J.
