Relapse rates were compared during 12 months or longer follow-up between 21 pediatric onset cases of multiple sclerosis (MS) seen at the Massachusetts General and 110 patients with adult-onset MS at the Brigham and Women’s Hospitals, Boston, MA. Pediatric-onset patients had a 1.13 annualized relapse rate that was significantly higher than that in the adult-onset group (0.40) (P<0.001). The adjusted rate ratio was 2.81. The increased relapse rate in pediatric-onset MS remained highly significant when controlled for disease-modifying treatment time, and when age at onset was treated as a continuous variable. Pediatric-onset MS has a more inflammatory disease course than adult onset MS. 
COMMENT. Pediatric-onset MS has a slower rate of progression than adult-onset disease, according to several reports. The discrepancy between higher relapse rate and slower long-term progression of pediatric-onset MS is unexplained.