Investigate the distribution of disease severity in pediatric-onset multiple sclerosis (MS).

Previous studies indicate pediatric-onset MS has a relatively benign disease course compared to adult-onset MS, however, these studies took into account disability measured by the EDSS scale, which focuses largely on locomotor deficits, which are less pronounced in children. There is a need to better characterize disability distribution and accrual in this population.

Data collected prospectively by the U.S. Network of Pediatric MS Centers was reviewed. Patients were stratified by the number of years from first symptoms of MS to EDSS assessment and an MS severity score (MSSS) was calculated per Roxburgh et al. criteria. For each year, the lowest and highest EDSS scores were calculated and then normalized by dividing 1+the number of available assessments. Scores from +/- one year were used to avoid stochastic fluctuations. This value was then multiplied by 10 to provide a range from 0-10 (MSSS = ). Pediatric MSSS scores represented percentiles amongst patients who had the disease for the same disease duration.

In total, 994 patients were reviewed, consisting of 4,349 unique data points. Range of disability in our pediatric cohort at one year from diagnosis was narrower than data published by Roxburgh et al., with EDSS of 0, 1, 1.5, and 2.0, corresponding to the 14^th, 40^th, 60^th, and 76^th percentiles compared to adults (7^th, 24^th, 43^rd, 59^th). This pattern was maintained at 2, 5, and 10 year’s disease duration (2 years: 14^th/5^th, 42^nd/20^th, 64^th/37^th, and 80^th/52^nd; 5 years: 13^th/3^rd, 38^th/13^th, 60^th/26^th, and 78^th/39^th; 10 years: 14^th/2^nd, 38^th/8^th, 56^nd/15^th, and 72^nd/21^st).

The distribution of disease severity by MSSS scoring in pediatric patients with MS is much more narrow than adults. This could have significant implications on clinical intervention analysis utilizing EDSS scoring alone.