20-year trends in multiple sclerosis prevalence, incidence and age at death in Lombardy, Northern Italy: a region-wide cohort study using administrative linked data

Background Multiple sclerosis (MS) is a leading cause of non-traumatic neurological disability in young adults. We assessed 20-year trends in MS prevalence, incidence and mean age at death in Lombardy, Italy, using population-wide linked administrative data. Methods We conducted a retrospective population-based cohort study including all regional residents aged 18 years or older between 2005 and 2024. MS cases were identified through an administrative algorithm. Annual crude and age-standardised incidence and prevalence rates were calculated overall and by sex and age group, using the 2025 WHO World Standard Population, including female-to-male ratios. Mean age at death was computed and stratified by sex. Temporal trends were analysed using joinpoint regression. Findings Among 10 million residents, MS incidence and prevalence increased from 8.2 (95%CI, 7.6–8.8) to 10.9 (10.2–11.6) and from 71.6 (70.0–73.2) to 152.4 (150.1–154.8) per 100,000 population, respectively, over the period 2005–2024. MS incidence was consistently higher among females and rose most markedly among adults 18–29-year +43.9%, from 12.4 (10.5–14.5; n=153) to 17.8 (15.5–20.4; n=217) per 100,000 and 30–39-year +42.9%, from 17.7 (15.7–19.9; n=283) to 25.3 (22.5–28.4; n=288). Overall age-standardised incidence declined non-significantly until 2015 (Annual Percentage Change (APC) −0.69%, 95% CI −7.61 to 0.90) followed by a significant increase thereafter (APC +2.84%, 95% CI 0.94–11.58). Incidence increased steadily in males (APC +1.54%, 95% CI 0.47–2.61), and, among females, rose significantly from 2013 onward (APC +2.30%, 95% CI 0.89–8.83). Over the study period, the female-to-male incidence rate ratio decreased from 2.4 (95% CI, 2.0–2.8) to 1.7 (1.5–1.9), whereas the corresponding prevalence ratio changed from 2.1 (95% CI, 2.0–2.2) to 1.9 (1.9–2.1). Mean age at death increased by about 6–10 years linearly since 2005, reaching 69.6 years (median 71.0, IQR 61.0–78.0, SD 11.7) among males and 73.8 years (75.0, 66.5–81.0, 10.7) among females in 2024. Interpretation MS incidence and prevalence increased over two decades, particularly among younger adults alongside older age at death. These findings may reflect changing disease risk, improved diagnostic sensitivity, and advances in treatment. Continuous surveillance using linked administrative data is essential for healthcare planning and resource allocation.