Endometriosis and Autoimmune Conditions: Insights into Shared Inflammatory Pathways

A recent large-scale study published in NPJ Women’s Health has uncovered a significant association between endometriosis and the subsequent development of autoimmune diseases within a two-year timeframe. This research, which examined data from over 1.5 million women, revealed that individuals diagnosed with endometriosis were nearly twice as likely to be diagnosed with a new autoimmune condition compared to those without the disease.

Endometriosis is a chronic inflammatory condition affecting approximately 10% of women of reproductive age. It is characterized by the presence of endometrial-like tissue outside the uterine cavity, often leading to debilitating pain and infertility. Autoimmune diseases—conditions in which the immune system erroneously attacks healthy tissue—impact roughly 8% of the general population, with women accounting for 80% of these cases.

Both endometriosis and autoimmune diseases involve systemic inflammation and immune system dysregulation. These shared features have led researchers to investigate potential links between the two conditions, including common immunological pathways and overlapping clinical presentations.

In this latest study, researchers analyzed claims data from two extensive U.S. healthcare databases—the Merative MarketScan Commercial Claims and Encounters (CCAE) and Multi-State Medicaid (MDCD) databases. The cohort included 332,409 women diagnosed with endometriosis and 1,220,932 matched controls without the condition. Within two years of an endometriosis diagnosis, 4.5% of women were diagnosed with at least one autoimmune disease, compared to 1.3% of controls.

The odds of being diagnosed with several autoimmune diseases—including rheumatoid arthritis, Hashimoto’s thyroiditis, systemic lupus erythematosus, multiple sclerosis, and pernicious anemia—were two to three times higher in women with endometriosis. For certain conditions such as Sjögren’s syndrome and myositis, the odds were up to six times higher. The study found that overall, the odds ratio (OR) of receiving an autoimmune diagnosis was approximately 2.0 for women with endometriosis versus controls.

Importantly, the researchers noted that this association does not establish causality. While chronic inflammation seen in endometriosis may contribute to autoimmune activation, other explanations are plausible. Physicians might more actively search for comorbid conditions such as autoimmune disease during diagnostic workups for endometriosis, thereby increasing detection. Additionally, autoimmune disease could drive symptom severity, leading to the delayed discovery of underlying endometriosis.

Genetic studies exploring correlations between endometriosis and autoimmune diseases such as rheumatoid arthritis and multiple sclerosis have produced mixed results. The current study did not find strong genetic overlap, further supporting the need for mechanistic studies.

This study’s use of a defined diagnostic window strengthens the temporal interpretation of findings, though limitations remain. The reliance on administrative claims data may introduce bias related to diagnostic coding practices and healthcare utilization. Nevertheless, the use of validated diagnostic phenotypes and statistical corrections for multiple comparisons bolsters the reliability of the results.

For clinicians, these findings underscore the need for heightened vigilance in monitoring patients with endometriosis for early signs of autoimmune disease. Earlier detection and management may mitigate long-term complications and improve quality of life. Moving forward, longitudinal studies with detailed clinical data and biomarker analysis are essential to elucidate the biological mechanisms underpinning these associations.