[Background of the new definitions for pediatric multiple sclerosis].

The characteristics of pediatric multiple sclerosis (MS), especially with the onset below ten years of age, are different from those of adult-onset MS. Polysymptomatic and encephalopathic features are frequently observed in pediatric MS. The MRI findings in a half of pediatric MS do not fulfill the McDonald criteria. There are different opinions on the prognosis of pediatric MS. Pediatric patients with the biphasic inflammatory demyelination and the good prognosis has been reported, which was previously classified in MS. For the purpose of distinguishing transient demyelinating syndromes from the lifelong disease, the new definitions for pediatric MS and related disorders were proposed. The surveillance of pediatric MS using the new definitions has been started in Japan.