Radiologically isolated syndrome: an uncommon finding at a university clinic in a high-prevalence region for multiple sclerosis

OBJECTIVE The improved availability of MRI in medicine has led to an increase in incidental findings. Unexpected brain MRI findings suggestive of multiple sclerosis (MS) without typical symptoms of MS were recently defined as radiologically isolated syndrome (RIS). The prevalence of RIS is uncertain. The aim of this study was to determine the prevalence of RIS at a university hospital in a region with a high prevalence for MS and describe the long-term prognosis of the identified patients. DESIGN Retrospective cohort study conducted in 2012. SETTING All brain MRI examinations performed at Karolinska University Hospital in Huddinge, Stockholm, Sweden during 2001 were retrospectively screened by a single rater for findings fulfilling the Okuda criteria. The sample year was chosen in order to establish the long-term prognosis of the patients identified. The examinations of interest were re-evaluated according to the Barkhof criteria by a neuroradiologist with long experience in MS. PARTICIPANTS In total 2105 individuals were included in the study. Ages ranged from 0 to 90 years with a median age of 48 years. Only one patient with RIS was identified, equivalent to a prevalence of 0.05% in the studied population, or 0.15% among patients aged 15-40 years. The patient with RIS developed symptoms consistent with MS within 3 months accompanied with radiological progression and was diagnosed with MS. CONCLUSIONS RIS, according to present criteria, is an uncommon finding in a tertiary hospital setting in a high-prevalence region for MS where awareness and clinical suspicion of MS is common. In order to study the prognosis of RIS, multicentre studies, or case-control studies are recommended.