Postmenopausal estrogen replacement therapy and the risk of developing systemic lupus erythematosus or discoid lupus.

Objective: There is evidence that estrogens play a role in the etiology of systemic lupus erythematosus (SLE), but this has not yet been shown for discoid lupus. We examined the association of postmenopausal estrogen use with the development of SLE and discoid lupus.
Methods: We did a case-control evaluation, using the UK based General Practice Research Database. We analyzed 41 cases with SLE, 34 cases with discoid lupus, and 295 age, sex and practice matched controls, and estimated relative risk estimates (odds ratios) in relation to estrogen exposure duration as well as total cumulative dose and estrogen type (alone or combined with progestogens).
Results: While short term estrogen exposure was not associated with increased risk, the risk of developing SLE (adjusted OR 2.8; 95% CI 0.9-9.0) or discoid lupus (adjusted OR 2.8; 95% CI 1.0-8.3) was significantly increased among current users who were exposed for 2 or more years. The adjusted RR estimate comparing longer term estrogen users and nonusers for all cases (SLE and discoid lupus combined) was 2.8 (95% CI 1.3-5.8; p < 0.01). A difference was found between longterm users of estrogens alone (OR 5.3; 95% CI 1.5-18.6) and those who used estrogens combined with progestogens (OR 2.0; 95% CI 0.8-5.0), compared to nonusers.
Conclusion: Our findings suggest that longer term use of postmenopausal estrogens plays a role in the etiology of both SLE and discoid lupus. There is a suggestion that progestogens may reduce the effect of estrogens on these autoimmune disorders.