LAUSR

BACKGROUND There is an absence of data from large population-based cohort studies on the incidence of radiologically isolated syndrome (RIS). We investigated the incidence of RIS and the subsequent risk for multiple sclerosis (MS). METHODS We conducted a population-based, retrospective cohort study using a data lake-based analysis of digitalized radiology reports. We screened all brain and spinal cord MRIs in people aged 16-70 during the years 2005-2010 (n=102 224) using optimized search terms to detect cases with RIS. The subjects with RIS were followed up until January 2022. RESULTS The cumulative incidence of RIS was 0.03% when all MRI modalities were included and 0.06% when only brain MRI was included according to MAGNIMS 2018 recommendation criteria. With the Okuda 2009 criteria, the respective figures were 0.03% and 0.05% (86% concordance). The overall risk for MS after RIS was similar 32% by using the MAGNIMS and 32% by using the Okuda definition of RIS. Individuals aged < 35.5 years exhibited the most significant predisposition to MS (80%), while those > 35.5 years had less than 10% risk of MS. MS diagnosed after RIS constituted 0.8% of the incident MS cases in the population during 2005-2010. CONCLUSIONS We provide a population-wide context for the incidence of RIS and its relationship to MS. MAGNIMS recommendations were only slightly more sensitive to detect RIS compared to Okuda criteria. RIS has a subtle effect on the overall incidence of MS, yet the risk for MS in individuals under the age of 35.5 years is substantial.