Global, regional and national trends in the epidemiology of rheumatoid arthritis from 1990 to 2021: an age-period-cohort effect analysis of the global burden of disease study 2021

Rheumatoid arthritis (RA) poses a significant global health challenge. This study examined trends in the incidence, prevalence and mortality of RA from 1990 to 2021 at global, regional and national levels, alongside age, period and cohort effects. Age-standardised rates (per 100 000 population) on RA incidence, prevalence and mortality were extracted from the Global Burden of Disease (GBD) study 2021. An age-period-cohort model estimated the overall annual percentage change (net drift), annual percentage change within each age group (local drift), and age/period/cohort relative risks. Globally, from 1990 to 2021, the age-standardised incidence rate (ASIR) and the age-standardised prevalence rate (ASPR) of RA increased; while age-standardised mortality rate (ASMR) decreased. Low-middle sociodemographic index (SDI) region showed the most notable increases in incidence and prevalence, while high SDI region had the largest decline in RA mortality. The South-East Asia Region exhibited the most significant increases in incidence and prevalence, and the African Region had the greatest mortality decline. Ireland reported the highest ASIR and ASPR in 2021, while the Republic of Honduras had the highest ASMR. Age effects peaked at 65-69 years for incidence and 80-84 years for prevalence, with the mortality risk increased with age. Period effects indicated rising incidence and prevalence but declining mortality, while younger birth cohorts showed increasing risks of incidence and prevalence and decreasing mortality risk. RA incidence and prevalence have risen globally, while mortality has declined. The regional, demographic and temporal variations underscore the need for targeted public health strategies to address the growing burden.