Screening Luxembourg's older general population for probable REM sleep behaviour disorder with a nationwide online survey

REM Sleep Behaviour Disorder (RBD) is a hallmark of the prodromal phase of α-synucleinopathies. We aimed to describe the prevalence of probable RBD and to assess its associations with demographics, cognition, and location in a large sample of older adults in Luxembourg, as a first step toward identifying individuals with RBD symptoms for future prodromal-marker assessment. In 2021, residents of Luxembourg aged 55–75 were invited to complete an online survey including the RBD Screening Questionnaire (RBDSQ); with a threshold of ≥ 7 defining screen-positive probable RBD (sppRBD). Screen-positive participants underwent a telephone interview, and those confirmed were categorised as telephone-assessed probable RBD (pRBD). Bayesian spatial mapping assessed the geographical distribution of pRBD, and logistic regression identified determinants of sppRBD and pRBD. Among 15,915 participants (54% male; median age 62 [IQR 58–67]), 12.4% had sppRBD. The telephone interview confirmed only 34.8% of these as pRBD, yielding a projected prevalence of 4.3%. Self-reported cognitive impairment, male sex, and Portuguese as questionnaire language were associated with pRBD, which showed heterogeneous geographical distribution. Online questionnaires may yield false positives, potentially reflecting e-health literacy issues; therefore, a confirmation step is essential. This analysis identifies individuals with RBD symptoms warranting further prodromal-marker assessment, a candidate group for, rather than a validated instance of, an at-risk-for-α-synucleinopathy cohort.