Objective: To investigate whether or not the disparity in disease progression in those with pediatric-onset compared with adult-onset multiple sclerosis (MS) is due to differences in relapse rates.
Design: Inception cohort. Mean follow-up times were 3.67 (standard deviation, 1.64) and 3.98 (standard deviation, 1.17) years in the pediatric and adult groups, respectively.
Setting: Comprehensive MS centers.
Patients: Patients with relapsing-remitting MS who were seen at the pediatric and adult MS centers at Massachusetts General and Brigham and Women's Hospitals, respectively, 12 months or less from onset of first symptom in July 2001 or later and were followed up for 12 months or longer. One hundred ten patients with adult-onset and 21 patients with pediatric-onset MS were included. Three eligible patients with adult-onset MS were excluded owing to incomplete records.
Main outcome measure: Annualized relapse rates were compared between pediatric-onset and adult-onset patients using the proportional means model.
Results: The annualized relapse rate in the pediatric-onset group was significantly higher than that in the adult-onset group (1.13 vs 0.40; P < .001) with an adjusted rate ratio of 2.81 (95% confidence interval, 2.07-3.81). When we controlled for time spent undergoing disease-modifying treatment in the analysis, the difference between the groups remained highly significant (adjusted rate ratio, 2.82; 95% confidence interval, 2.08-3.83; P < .001). When age at disease onset was treated as a continuous variable, a highly significant association between age and relapse rate was observed (P < .001).
Conclusions: Relapses are more frequent in patients with pediatric-onset compared with adult-onset MS in the disease-modifying treatment era. This finding suggests that patients with pediatric-onset MS experience a more inflammatory disease course than patients with adult onset of the disease.