conversion from radiologically isolated syndrome to multiple sclerosis

background: the aim of this study was to estimate the conversion rate from radiologically isolated syndrome (ris) to definite multiple sclerosis (ms). methods: during a mean (standard deviation [sd]) follow-up period of 17.4 (5.4) (range 8-29) months, 25 subjects with ris and without neurological symptom aged 22-45 year from a single-center have been examined for the occurrence of definite ms. the mean (sd) age of participants was 35.1 (6.2) years at first brain magnetic resonance imaging (mri). the definite ms were assessed using the revised mcdonald’s criteria (2010). results: six of 25 patients developed clinical symptom consistent with criteria for definite ms. the conversion rate from ris to definite ms was 1.5 (95% confidence interval [ci] 0.54, 3.17) per 100 person-months based on 480 person-months of follow-up. multivariate analysis revealed that presence of contrast-enhancing lesions on the initial mri was marginally significantly associated with ms (hazard ratio 1.83, 95% ci 0.98, 3.45, p = 0.060). conclusions: this is the first estimate of conversion rate from ris to definite ms in iran. the conversion rates from ris to definite ms in these participants are high and intensive follow-up and intervention strategies are recommended for these high-risk individuals. a larger study is warranted to assess this risk in greater detail.