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). The RBDSQ-J was administered to 52 consecutive patients with iRBD diagnosed according to criteria in the ICSD-2 (mean age 66.4 years; 36 males, 16 females), 55 consecutive OSAS patients who had responded well to CPAP therapy (mean age 63.1 years; 44 males, 11 females) after a diagnosis of RBD was ruled out by history and PSG and 65 apparently healthy subjects (mean age 64.6 years; 37 males, 28 females).

The mean RBDSQ-J scores for the iRBD group, the OSAS group and the healthy subjects were 7.5, 1.9, and 1.6 points, respectively. Sensitivity and specificity using a cut-off of 4.5 were high in differentiating the iRBD group from healthy subjects or the OSAS group. An RBDSQ-J score cut-off of 5.0 was considered useful for differentiating the iRBD group from the healthy subjects or the OSAS group. Cronbach's alpha for the entire RBDSQ-J was 0.866. The RBDSQ-J score had no correlation with the duration of RBD (mean disease duration in the iRBD group from symptom onset was 4.6 years, range 0.2 to 18 years). Answers to some items varied or had lower sensitivity. For example, for items 5, 6.2, and 6.3 a bed partner would be needed to provide answers, and the situations referred to in items 6.4 and 8 were often obscure. In evaluation of reliability, items that enlarged the kappa coefficient were 1, 2, 5 and 6.1 for iRBD. It can be proposed that future evaluations should use weighted scores for RBDSQ-J items, which may improve the accuracy of the questionnaire. The RBDSQ-J has high sensitivity, specificity, and reliability and would be applicable as a screening method for iRBD in an elderly Japanese population. Early-onset patients (^50 years) were reported to have significantly more past and present psychiatric diagnoses and antidepressant usage than late-onset patients (>50 years) (Teman et al., 2009). It may be necessary to validate the RBDSQ-J in early-onset patients.

Nomura et al. evaluated the usefulness of the RBDSQ-J among patients with PD (Nomura et al., 2011). A total score of 6 points on the RBDSQ-J represented the best cut-off value for detecting RBD. This cut-off value for RBD secondary to PD was approximately 1 point higher than that reported for iRBD in studies performed by Stiasny-Kolster et al. and Miyamoto et al. However, the cut-off value with the RBDSQ-J for PD patients would become equal to the above-indicated value for iRBD patients if item 10 were removed. Nomura et al. showed that the RBDSQ-J may be useful for detecting RBD among a PD population regardless of the RBD symptoms. In addition, positivity for item 6.1 might represent a key criterion for analyzing populations with non-violent RBD.

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