Background. Paediatric-onset MS (POMS) has a unique clinical profile compared to the more prevalent adult-onset MS. For this study, we aimed to determine the demographic and clinical characteristics of POMS in Poland as well as addressing some of its epidemiological aspects. Methods. A retrospective study was conducted based on the Polish Multiple Sclerosis Registry, considering a population of children and adolescents with MS (age ≤ 18 years). Data were collected by all 13 centres across Poland specializing in diagnosing and treating POMS. The actual course of the disease and its clinical properties were compared between child (≤12 years) and juvenile (>12 years) patients. MS onset and its prevalence were assessed at the end of 2019, stratified by age range. Results. A total of 329 paediatric or juvenile patients (228 girls, 101 boys) with a clinically definite diagnosis of MS, in conformity with the 2017 McDonald Criteria, were enrolled. For 71 children (21.6%), the first symptoms appeared before the age of 12. The female: male ratio increased with age, amounting to 1:1 in the ≤12 years group and to 2.9:1 in the >12 years group. In most cases, the disease had multi-symptomatic onset (31.3%), and its course was mostly of a relapsing−remitting character (95.7%). The initial Expanded Disability Status Score for both groups was 1.63 ± 1.1, whereas the annual relapse rate was 0.84 during the first 2 years. The time between the onset of symptoms and diagnosis was longer in the younger patients (8.2 ± 4.2 vs. 4.6 ± 3.6 months; p < 0.005). On 31 December 2019, the age-adjusted prevalence standardized to the European standard population was 5.19/100,000 (95% CI, 4.64−5.78). Significantly higher prevalence was noted in the 13−18 years group (7.12; 95% CI, 6.64−7.86) than in the 9−12 years group (3.41; 95% CI, 2.98−3.86) and the <9 years group (0.56; 95% CI, 0.46−0.64; p < 0.001). Conclusion. POMS commencing at the age of ≤12 years is rare, differing significantly from the juvenile-onset and adult MS in terms of clinical characteristics, course, and incidence, as stratified by gender.
Keywords: adolescent-onset; childhood-onset; clinical features; paediatric-onset multiple sclerosis; prevalence.