Hydroxychloroquine May Reduce Risk for Endometriosis in Patients With SLE

In a population-based cohort study, researchers assessed the relationship between hydroxychloroquine treatment and endometriosis in patients with systemic lupus erythematosus.

Continuous treatment with hydroxychloroquine (HCQ) may reduce the risk for endometriosis in patients with systemic lupus erythematosus (SLE), according to study results published in Lupus.

Studies have shown that women of reproductive age with SLE may be at elevated risk of developing endometriosis.

To assess the effect of HCQ in patients with SLE with endometriosis, the researchers conducted a population-based, retrospective cohort study using data collected from the Longitudinal Health Insurance Database in Taiwan. Women who were newly diagnosed with SLE between 2000 and 2012 were eligible for inclusion in the study.

The primary exposure was HCQ treatment, defined as receiving continuous HCQ at any dosage at baseline. Patients with HCQ exposure were stratified into 2 groups: “low dose” HCQ, or receiving HCQ for less than 90 days at baseline; and “high dose” HCQ, or receiving HCQ for 90 days or more at baseline. Patients receiving treatment with low-dose HCQ were age-matched in a 1:2 ratio with patients who received high-dose HCQ. Cox proportional hazard models were used to assess the impact of HCQ exposure on the incidence of endometriosis.

The study cohort included 742 women who were diagnosed with SLE, among whom185 were in the low-dose HCQ group and 557 were in the high-dose HCQ group. After age-matching, the final cohort included 555 patients (185 using low-dose HCQ and 370 using high-dose HCQ). Demographic characteristics were comparable between dose groups.

The high-dose HCQ group had longer prior hospital stays compared with the low-dose group. The most frequently prescribed non-HCQ medications in the total cohort were corticosteroids, oral antihypertensives, and azathioprine. The calculated incidence rates of endometriosis were 44.54 and 90.03 per 100,000 person-months in the high- and low-dose HCQ groups, respectively. Compared with the low-dose group, the high-dose group had a conditional hazard ratio (aHR) for incident endometriosis of 0.482 (95% CI, 0.191-1.213), suggesting reduced risk.

While the relationship in the total cohort was not statistically significant, sensitivity analyses revealed more substantial associations. For patients receiving treatment with additional immunosuppressive drugs, high-dose HCQ was associated with significantly lower risk for incident endometriosis (aHR, 0.267; 95% CI, 0.072-0.997). Similarly, among patients with concomitant corticosteroid use, high-dose HCQ appeared to significantly reduce the risk for endometriosis (aHR, 0.355; 95% CI, 0.135-0.934)

Results from this study suggested that HCQ treatment may reduce the risk for incident endometriosis in women with SLE. Overall, the incidence rate of endometriosis in the cohort treated with HCQ was lower than incident rates reported in prior studies of SLE. Greater treatment duration appeared to further reduce endometriosis risk.

Study limitations included the small number of endometriosis cases and the lack of data on certain lifestyle variables and biologics use.

“Clinically, we suggest that patients [with] SLE should be treated with HCQ as standard therapy, especially in patients with risk [for] endometriosis,” the researchers concluded.


Chen FY, Chen SW, Chen X, Huang JY, Ye Z, Wei JC. Hydroxychloroquine might reduce risk of incident endometriosis in patients with systemic lupus erythematosus: a retrospective population-based cohort study. Lupus. Published online July 14, 2021. doi:10.1177/09612033211031009