Age and sex as key determinants of multiple sclerosis incidence in Spain: a comprehensive analysis using the global burden of disease database (1990-2019).

aimTo explore trends in multiple sclerosis incidence rates in Spain between 1990 and 2019.

methodsWe use data from the Global Burden of Disease Study 2019 to calculate age-standardised incidence rates of multiple sclerosis and identify significant changes over time using the Joinpoint regression model. We also use the Age-Period-Cohort model to understand the separate influences of age, historical period, and birth cohort on these trends.

resultsBetween 1990 and 2019, Spain reported 31,152 cases of multiple sclerosis, with an average annual growth rate of 1.3%, slightly higher in men (1.40%) than in women (1.28%). Joinpoint analysis revealed non-parallel trends of incidence between sexes, with men experiencing increases and declines along five differentiated periods, while women showed increasing rates until 2015, followed by stabilization. The incidence of multiple sclerosis increased over time in both sexes achieving an average annual increase of 1.6% for men and 1.4% for women. Individuals born in the early to mid-20th century experienced a different trajectory compared to later generations. For both sexes, their MS risk steadily climbed from the mid-20th century, reaching a peak in the 1970s and 1980s for men and potentially later in the 1990s for women. This peak was then followed by a plateauing of risk in subsequent years.

conclusionsOverall, this study offers valuable insights into MS incidence trends in Spain, highlighting sex disparities, age effects, and generational patterns. Further research is needed to understand the complex interplay of age, period, and cohort effects, as well as regional and environmental factors contributing to risk of new cases of multiple sclerosis.