IMPACT OF PARAMAGNETIC RIM LESIONS ON CONVERSION TO MULTIPLE SCLEROSIS IN PATIENTS WITH RADIOLOGICALLY ISOLATED SYNDROME

Introduction: Radiologically Isolated Syndrome (RIS) represents a preclinical stage of multiple sclerosis (MS) characterized by incidental MRI findings suggestive of MS in the absence of neurological symptoms. Identifying imaging biomarkers that predict conversion to MS remains a major clinical challenge. Paramagnetic rim (PR) lesions have emerged as markers of chronic active inflammation in MS; however, their prognostic value in RIS remains unclear. This study aimed to evaluate the impact of PR lesion presence and PR burden on the risk of conversion from RIS to MS. Methods: This retrospective, single-center observational cohort study included 46 patients diagnosed with RIS who had susceptibility-weighted imaging (SWI) sequences available at baseline. PR lesions were defined as hypointense rims on SWI. PR presence was analyzed as a binary variable, and PR burden was categorized according to lesion count. The primary outcome was conversion to MS according to the 2017 McDonald criteria. Associations between PR variables and MS conversion were assessed using odds ratios (ORs) with 95% confidence intervals (CIs). Results: During follow-up, 20 patients (43.5%) converted to clinically definite MS. MS conversion occurred in 63.6% of PR-positive patients compared with 25.0% of PR-negative patients (p<0.001). PR positivity was associated with a significantly increased risk of MS conversion (OR: 5.25; 95% CI: 1.48–18.66). Analysis of PR burden demonstrated a stepwise increase in MS conversion rates with higher PR counts, reaching 77.8% in patients with ≥3 PR lesions. Conclusion: The presence of PR lesions and increasing PR burden are strongly associated with a higher risk of conversion to MS in patients with RIS. PR lesions may serve as clinically meaningful imaging biomarkers for risk stratification and early identification of high-risk individuals in the preclinical stage of MS