In a previous study, women with endometriosis were found to be at a 7-24-fold increased risk of multiple sclerosis (MS), systemic lupus erythematosus (SLE) and Sjögren syndrome (SS). We examined these associations in a large population-based cohort study.
We followed 37 661 women registered with endometriosis in the Danish Hospital Discharge Register 1977-2007 for subsequent hospitalizations with MS, SLE or SS. As measures of relative risk, we used ratios of observed to expected incidence rates of first hospitalizations for MS, SLE and SS among women with endometriosis, i.e. standardized incidence ratios (SIR) with accompanying 95% confidence intervals (CIs).
During slightly more than 456 000 person-years of follow-up, we identified 130, 54 and 86 cases of MS, SLE and SS, respectively, yielding SIRs of 1.2 (95% CI 1.05-1.5) for MS, 1.6 (1.2-2.1) for SLE and 1.6 (1.3-2.0) for SS. In a supplementary analysis restricted to 9191 women with laparoscopy or laparotomy confirmed endometriosis, associations were unchanged for MS (SIR = 1.4; 1.04-1.9), but lost statistical significance for SLE (SIR = 1.1; 0.6-2.1) and SS (SIR = 1.4; 0.9-2.3).
Our national cohort-based findings do not support prior claims of markedly increased risks of MS, SLE and SS in women with endometriosis. However, whether women with endometriosis are truly at a modestly (20-60%) elevated risk of one or more of the studied autoimmune diseases must await clarification in future large-scale prospective studies.