Autoimmune Diseases and Incident Spontaneous Subarachnoid Hemorrhage: A Swedish Population-Based Cohort Study

Compelling evidence documents an association between autoimmune diseases and several types of cardiovascular diseases. Knowledge on whether autoimmune diseases may increase the risk of subarachnoid hemorrhage (SAH), a rare but severe type of cerebrovascular event, is very limited. The aim of this study was to determine the association between autoimmune diseases and SAH.

We conducted a nationwide cohort study including individuals who were parents of all live births recorded in the Swedish Medical Birth Register during 1973-2014 and who were alive, resided in Sweden, and had no history of SAH at study baseline. We obtained data on autoimmune diseases, SAH, and covariates through linkage to several population-based registers and followed participants from January 1, 2001, until SAH diagnosis, death, emigration, or December 31, 2023. We used Cox proportional hazards models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for SAH in relation to autoimmune diseases.

Among the 3,824,528 study participants (mean age at baseline 38.1 (±13.2) years, 55.2% female), 608,043 (15.9%) had a record of any autoimmune disease before or during the study period; 10,311 (0.3%) were diagnosed with SAH over the follow-up period of 83.5 million person-years. Overall, any autoimmune disease was associated with an increased risk of SAH (HR = 1.18; 95% CI 1.11-1.25). Several categories, as well as some specific autoimmune diseases, that is, type 1 diabetes (HR = 1.36; 95% CI 1.15-1.61), rheumatoid arthritis (HR = 1.29; 95% CI 1.10-1.50), systemic lupus erythematosus (HR = 1.49; 95% CI 1.01-2.21), psoriasis vulgaris (HR = 1.18; 95% CI 1.04-1.33), multiple sclerosis (HR = 1.35; 95% CI 1.02-1.78), primary biliary cirrhosis (HR = 2.66; 95% CI 1.57-4.49), and IgA nephropathy (HR = 1.42; 95% CI 1.08-1.87), were associated with an increased risk of SAH.

This study suggested that a broad range of autoimmune diseases may be involved in the etiology of SAH. If confirmed by future research, the results may inform the development of targeted SAH prevention strategies for individuals with autoimmune diseases; however, reliance on register-based diagnoses and the lack of detailed lifestyle information such as smoking may have led to misclassification and residual confounding.