Disease-modifying antirheumatic drugs and risk of thyroxine-treated autoimmune thyroid disease in patients with rheumatoid arthritis.

BACKGROUND: Autoimmune thyroid disease (AITD) and rheumatoid arthritis (RA) share a genetic background, and the prevalence of AITD in RA patients is increased. Whereas immunomodulatory treatments are used in RA, they are rarely used in AITD.

OBJECTIVES: We hypothesized that disease-modifying antirheumatic drugs (DMARDs) as used in RA might lower the risk of incident AITD.

METHODS: A nationwide cohort study including 13,731 patients with new-onset RA from the Swedish Rheumatology Quality Register 2006-2018 and 63,201 matched general population comparators linked to national registers to identify AITD. We estimated relative risks (hazard ratios) of AITD after RA diagnosis in RA patients compared to the general population, and in relation to DMARD treatment, using Cox regression.

RESULTS: Following RA diagnosis, 321 (2.3%) of the RA patients and 1838 (2.9%) of the population comparators developed AITD, corresponding to an incidence of 3.7 versus 4.6 per 1000 person-years, hazard ratio, 0.81; 95% CI, 0.72-0.91. The decreased risk of incident AITD among RA patients compared to the general population was most pronounced among biologic DMARD (bDMARD) treated patients, with a hazard ratio of 0.54; 95% CI, 0.39-0.76. Among RA patients, subgrouped by bDMARD use, TNF-inhibitors were associated with the most pronounced decrease, hazard ratio, 0.67; 95% CI, 0.47-0.96.

CONCLUSIONS: In contrast to the increased prevalence of AITD in RA patients at diagnosis, our results indicate that the risk of AITD decreases following RA diagnosis. This decrease is especially pronounced in RA patients treated with bDMARDs. These findings support the hypothesis that DMARDs might have a preventive effect on AITD.