Pediatric-onset multiple sclerosis in Finland

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.

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.

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.

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.