SAN DIEGO, CACurrent use of postmenopausal hormone therapy was associated with a decreased risk of ACPA-positive—but not ACPA-negative—rheumatoid arthritis, a study presented at the 2013 ACR/ARHP Annual Meeting has shown.

“The striking difference in the results for ACPA-positive and ACPA-negative rheumatoid arthritis adds further evidence to the notion that rheumatoid arthritis consists of two different entities with partly different etiology,” noted Cecilia Orellana, a PhD student at the Institute of Environmental Medicine, Karolinska Institutet in Stockholm, Sweden.

Noting the literature “is somewhat contradictory” with respect to the role hormonal/reproductive factors and use of postmenopausal hormone therapy may play in risk of rheumatoid arthritis—including increased risk, decreased risk, and no association—the investigators studied the association in women 50—70 years of age, stratified by presence/absence of anti-citrullinated protein antibodies (ACPA).

After analyzing data from the Swedish population-based Epidemiological Investigation of Rheumatoid Arthritis case-control study, they included 467 incident postmenopausal female cases and 935 randomly selected controls (matched by age and residential area) between 2006—2011. Of the cases, 239 (62.9%) were ACPA-positive.

Participating cases and controls completed an identical questionnaire about postmenopausal hormone therapy use. Current and past users of postmenopausal hormone therapy were compared with never users to obtain odds ratios (ORs) with 95% confidence intervals (CI) by means of unconditional logistic regression models.

They observed a decreased risk of developing ACPA-positive rheumatoid arthritis among current users compared with never users of postmenopausal hormone therapy (OR 0.5; 95% CI 0.3–0.9). However, no association was found when past vs. never users were compared (OR 1.2; 95% CI 0.8–1.7). Among women with ACPA-negative rheumatoid arthritis, no association was found among current (OR 1.0; 95% CI 0.6–1.8) or past (OR 1.2; 95% CI 0.8–2.0) users of postmenopausal hormone therapy.

The investigators concluded, “Further research is needed in order to explore the biological mechanisms behind our findings.” Additional exploration of post-menopausal hormone therapy and the prognosis of rheumatoid arthritis is planned.