Pediatric-onset multiple sclerosis in Finland.

INTRODUCTION: Although there are extensive data on multiple sclerosis (MS) in adults, the epidemiology and clinical features of pediatric-onset multiple sclerosis (POMS) in Finland are unknown. SUBJECTS: and methods: Individuals under 18 years of age diagnosed with clinically isolated syndrome (CIS) or MS were identified from the MS registries of Tampere and Helsinki University Hospitals, based on the ICD-10 classification. The data were extracted from the electronic patient records (EPRs) and MS registries. RESULTS: A total of 73 children with CIS were identified. Among these, 34 (47%) were diagnosed with MS before the age of 18, and an additional 8 (11%) by the age of 28. The median time from CIS to a diagnosis of MS in those diagnosed before 18 was 6 months. CIS phenotypes included optic neuritis (ON) in 23/73 (32%), acute disseminated encephalomyelitis (ADEM) in 10/73 (14%), transverse myelitis (TM) in 9/73 (12%), internuclear ophthalmoplegia (INO) in 5/73 (7%) and other or undefined monofocal presentations in 15/73 (21%) and multifocal presentations in 11/73 (15%). The prevalence of POMS in our cohort was 5.5 per 100,000, with an incidence ranging from 0.16 to 0.81 per 100,000. CONCLUSION: POMS is rare in Finland. Although ON was seen in 32% of all cases of CIS, other mono- and multifocal manifestations predominated in those who developed POMS. Unlike in adults, ADEM can also rarely develop into MS in pediatric patients.