TOPLINE:

Patients with rheumatoid arthritis (RA) in a large Swedish population cohort show a reduced incidence of autoimmune thyroid diseases, such as hypothyroidism or hyperthyroidism, after being diagnosed with RA, with the effect being more pronounced among those treated with disease-modifying anti-rheumatic drugs (DMARDs), particularly TNF-inhibitors.

Although DMARDs are commonly used in the treatment of RA, the drugs are rarely used to treat autoimmune thyroid diseases. The new results support theories raised in previous smaller studies that DMARDs could have a protective effect against thyroid disease.

METHODOLOGY:

• The study involved 13,731 patients with new-onset RA who were listed in the Swedish Rheumatology Quality Register between 2006 and 2018.

• The patients were matched for sex, age, and residential area with up to five reference individuals in the general population of 63,201 comparators.

• Overall, patients with RA were 64.7% female, with a mean age of 59. They were followed up with their matched comparators until the development of autoimmune thyroid disease, death, emigration, or the end of the study period, December 2019.

• The relative risks of autoimmune thyroid disease following a diagnosis of RA and with treatment with DMARDs were compared with those risks in the general population.

• Participants with a non-autoimmune cause for thyroxine prescription were excluded, as were those with an autoimmune thyroid disease at the time of RA diagnosis.

TAKEAWAY:

• Following their RA diagnosis, 321 (2.3%) of patients developed an autoimmune thyroid disease, compared with 1838 (2.9%) in the general population comparators, representing an incidence of 3.7 vs 4.6 per 1000 person-years (hazard ratio [HR], 0.81).

• The lower incidence of autoimmune thyroid disease was more pronounced with longer RA duration. For instance, at 10-14 years after an RA diagnosis, the incidence was 2.9 vs. 4.5 autoimmune thyroid disease events per 1000 person-years, respectively (HR, 0.64).

• The decreased risk of incident autoimmune thyroid disease among RA patients compared with the general population was strongest among patients treated with  biologic DMARDs (bDMARD), with an HR of 0.54.

• The reduced incidence of autoimmune thyroid disease with bDMARD use was most pronounced among users of TNF-inhibitors (HR, 0.67).

• The lower incidence of autoimmune thyroid disease following a diagnosis of RA contrasts with previous studies showing an increased risk for thyroid disease associated with RA.

• However, the decreased risk of thyroid disease following bDMARD treatment supports the theory that immunomodulatory treatment could also have an effect of blunting the inflammatory processes that can lead to overt clinical autoimmune thyroid disease.

IN PRACTICE:

“To our knowledge, no previous study has investigated whether the risk of new-onset autoimmune thyroid disease is affected by RA treatment in early RA,” the authors report.

“Our results demonstrate that compared to the general population, patients with RA treated with bDMARDs, TNF-inhibitors in particular, are at decreased risk of developing autoimmune thyroid disease, a finding that calls for replication and may open for drug-repurposing studies,” they note.

SOURCE:

The study was conducted by first author Kristin Waldenlind, PhD, of the Department of Medicine, Solna, Division of Clinical Epidemiology, Karolinska Institutet, Stockholm, Sweden, and colleagues. It was published online November 27 in Journal of Internal Medicine.

LIMITATIONS:

The study lacked details on participants’ thyroid autoantibody and hormone levels.

The presence of autoimmune thyroid disease was determined based on prescriptions for thyroxine, hence the authors cannot exclude the possibility of a lower threshold for thyroxine prescription among patients treated with DMARDs.

Information was not available on potential risk factors for RA and autoimmune thyroid disease that might have introduced confounding, such as smoking or obesity.

DISCLOSURES:

The study received funding from the Swedish Research Council, the Swedish Heart Lung Foundation, Vinnova, and Region Stockholm/Karolinska Institutet (ALF). The authors’ disclosures are detailed in the published study.

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