Objectives Autoimmunity may play a role in endometriosis. The association between endometriosis and RA remains unknown. This study was conducted to identify any evidence for this relationship. Methods This 13-year, nationwide, population-based, retrospective cohort study analysed the risk of RA in a cohort of individuals with endometriosis. We investigated the incidence of RA among patients with endometriosis using data from the Longitudinal Health Insurance Database 2000, which is maintained by the Taiwan National Health Research Institutes. We used propensity scores to match comorbidities in the two cohorts. Kaplan–Meier analysis and Cox proportional hazard model were employed to analyse the association between endometriosis and RA among patients with different potential risks. Results Patients with endometriosis [adjusted hazard ratio (HR) 1.75, 95% CI 1.27, 2.41], aged ≥45 years (adjusted HR 1.50, 95% CI 1.06–2.13) and with autoimmune disease (adjusted HR 6.99, 95% CI 2.84–17.21) had a significantly higher risk of RA. The analyses also showed that when stratified by age, comorbidities and medication use, the risk of RA in patients with endometriosis was also higher than in those without endometriosis. Conclusions This 14-year, nationwide, population-based retrospective cohort study revealed that patients with endometriosis have a higher risk of RA. In the clinical management of patients with RA, rheumatologists should be especially mindful of the possibility of underlying endometriosis.

Background: Moderate to severe atopic dermatitis (AD) is difficult to treat. There are rare reports on the treatment of moderate to severe AD by lowering serum IgE with a combination of methotrexate (MTX) and azathioprine (AZA) and hence improving symptoms. Objective: This study aimed to improve AD symptoms by lowering serum IgE with a combination therapy of MTX and AZA. Design: Retrospective cohort study of patients treated during 2013 and 2019. Setting: Patients recruited from a tertiary care university hospital in Taiwan. Participants: Sixty-five (case group) and 36 (control group) patients with moderate to severe AD, aged between 10 and 77 years. Measurements: Patients in the case group received a combination of MTX (15 mg weekly) and AZA (150 mg daily) for 1 to 5 years. Patients in the control group received any therapies other than this combination. Serum total IgE levels were checked periodically in both groups. Results: Serum total IgE was markedly reduced in the case group. For example, the cumulative success rates of a 50% IgE reduction in the case group in year 1 and year 5 were 69.2% and 98.5%, respectively, compared to 10.0% and 18.2% in the control group (hazard ratio 14.8; p < 0.001). At the end of year 4, the cumulative success rate of IgE reduction to below the normal range was 41.1% in the case group and 3.4% in the control group (hazard ratio 6.71; p = 0.033). Regarding adverse events, the rates of abnormal white blood cell counts, hemoglobin, platelet counts, and alanine aminotransferase were not increased in the case group compared to the control group. Conclusion: Combination therapy with MTX and AZA was effective in treating patients with intractable AD by reducing their serum total IgE levels.