Prevalence of idiopathic REM behavior disorder: a systematic review and meta-analysis.

STUDY OBJECTIVES To provide an overall estimate of the prevalence of idiopathic REM Sleep Behavior Disorder (iRBD). METHODS Two investigators have independently searched the PubMed and Scopus databases for population-based studies assessing the prevalence of iRBD. Data about type of diagnosis (polysomnographic diagnosis, defined iRBD [dRBD]; clinical diagnosis, probable RBD [pRBD]), continent, age range of the screened population, quality of the studies, sample size, screening questionnaires and strategies have been gathered. A random effect model was used to estimate the pooled prevalence. Heterogeneity was investigated with subgroup analysis and meta-regression. RESULTS From 857 articles found in the databases, 19 articles were selected for the systematic review and meta-analysis. According to the type of diagnosis, five studies identified dRBD cases given a pooled prevalence of 0.68% (95%CI 0.38-1.05) without significant heterogeneity (Cochran's Q p=0.11; I 2 = 46.43%). Fourteen studies assessed the prevalence of pRBD with a pooled estimate of 5.65% (95%CI 4.29-7.18) and a significant heterogeneity among the studies (Cochran's Q p<0.001; I 2 = 98.21%). At the subgroup analysis, significant differences in terms of prevalence were present according to the quality of the studies and, after removing two outlaying studies, according to the continents and the screening questionnaire used. Meta-regression did not identify any significant effect of the covariates on the pooled estimates. CONCLUSION Prevalence estimates of iRBD are significantly impacted by diagnostic level of certainty. Variations in pRBD prevalence are due to methodological differences in study design and screening questionnaires employed.