Trends and cross-country inequalities in the global burden of subarachnoid hemorrhage, 1990–2021: a population-based study

Objective This study aimed to analyze global and regional trends in the burden of subarachnoid hemorrhage (SAH) from 1990 to 2021, focusing on incidence, prevalence, disability-adjusted life years (DALYs), and mortality, and to examine socioeconomic inequalities across 204 countries and territories using Global Burden of Disease (GBD) data. Methods Utilizing GBD 2021 data, we assessed SAH burden by incidence, prevalence, DALYs, and mortality, stratified by Socio-Demographic Index (SDI), sex, and region. Age-standardized rates were calculated to ensure comparability. Socioeconomic inequalities were evaluated using the Slope Index of Inequality (SII) and Concentration Index (CII). Spearman correlation analyses explored associations between SAH burden and SDI. Results From 1990 to 2021, global SAH incident cases increased from 508,789 (95% UI 441,504–587,616) to 697,486 (95% UI 614,334–795,785), and prevalent cases rose from 4.90 million (95% UI 4.42–5.39 million) to 7.85 million (95% UI 7.16–8.58 million). Age-standardized incidence, prevalence, DALY, and mortality rates declined significantly, from 11.69 to 8.33, 109.90 to 92.17, 275.85 to 125.20, and 9.54 to 4.18 per 100,000, respectively. East Asia showed the largest declines (e.g., incidence from 17.74 to 7.89 per 100,000), while Andean Latin America had the highest burden (2021 prevalence: 172.03 per 100,000). Females had higher incidence and prevalence but lower DALYs and mortality. Middle SDI regions exhibited the largest case increases and rate declines. Socioeconomic inequalities worsened, with 2021 DALY SII at −47.27 (95% CI −71.58, −22.97) and mortality SII at −1.33 (95% CI −2.14, −0.51), indicating a shift in burden toward lower-income groups. SAH burden showed weak negative correlations with SDI, stronger for DALYs ( r = −0.3541, p 0.001) and mortality ( r = −0.3058, p 0.001). Conclusion Despite increasing absolute SAH cases due to population growth and aging, age-standardized rates declined, reflecting improved risk factor management and healthcare. However, persistent regional disparities and growing socioeconomic inequalities, with heavier burdens in low SDI regions and lower-income groups, underscore the need for targeted interventions, enhanced healthcare access, and further research into region-specific risk factors to reduce the global SAH burden and address health inequities.