This study aimed to analyze the factors that predict the conversion of radiologically isolated syndrome (RIS) patients to multiple sclerosis (MS), and the validity of the two RIS diagnostic criteria.

Okuda et al. introduced the RIS criteria for the first time in 2009. In 2018, the MAGNIMS group proposed less stringent criteria. There are no studies comparing these two criteria.

All participants with suspected demyelinating brain MRI lesions were included in this study. Patient data was collected including demographics, clinical and cerebrospinal fluid (CSF) parameters, and MRI lesion characteristics. All MRI images were reevaluated by two MS specialists and a neuroradiologist. Multi-parameter Cox-regression method was used during the analyses.

A total of 130 patients (30 mRIS, 65 Okuda and mRIS, 35 nonRIS) from seven centers were included into the study. Fifty percent of the patients converted into MS after 8.59 years (95% CI: 3.95-13.22). The conversion rate of the three groups were comparable (p=0.18). Presence of oligoclonal bands in the CSF (OCB) (HR=0.09, p=0.02), elevated IgG index (HR=0.08, p=0.02), and presence of spinal MRI lesion (HR= 0.23, p=0.001) predicted conversion to MS. Male gender (HR=1.05, p=0.89) and age less than 37 (HR=0.56, p=0.21) were not predictive of conversion to MS.

Our findings indicates that baseline spinal lesions, an elevated IgG index, and OCB are the best predictors of conversion to MS. Considering conversion to MS, we found no difference between patients who fulfilled the Okuda or modified RIS criteria. It is necessary to explore new parameters that will improve the sensitivity and specificity of the present diagnostic criteria for RIS.