The Burden of Multiple Sclerosis in Japan from 1990 to 2021 and Predictions to 2050 Based on the Global Burden of Disease Study 2021

INTRODUCTION: Global increases in multiple sclerosis (MS) prevalence and incidence have been observed, yet Japan's longitudinal trends and future burden remain understudied. METHODS: This study analyzed MS incidence, mortality, and disability-adjusted life years (DALYs) in Japan from 1990 to 2021, and projected burden to 2050 using age-period-cohort modeling and Bayesian meta-regression. RESULTS: Results showed a 50.2% rise in age-standardized prevalence ratios (from 7.622 to 11.452 per 100,000), mainly driven by a 59.2% increase among females (from 10.853 to 17.282 per 100,000). Projections indicate an increase to 10.12 per 100,000 by 2050, with females remaining disproportionately affected (female-to-male ratio: 2.18:1). Disability accounted for 71.2% of total DALYs in 2021, especially among women aged ≥80 years, who experienced a 446% increase in years lived with disability. Regional disparities persisted, with northern prefectures showing higher prevalence and DALYs. Incidence peaks shifted to older ages, and female incidence remained 1.5-2.0 times higher than males after 2000. CONCLUSION: Although Japan remains a low-incidence country, the MS burden is rising due to increasing disability, female predominance, and regional disparities, highlighting the need for targeted screening, resource allocation to high-risk areas, and elderly focused care.