Risk of Thyroxine-treated autoimmune thyroid disease associa
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Autoimmune thyroid disease ([AITD] including hypothyroidism and hyperthyroidism) is the most common organ-specific autoimmune disorder and is more prevalent among patients with rheumatoid arthritis (RA). Real-world studies on when and how this increased risk of AITD develops, in association with the time before or after the onset of RA, are lacking.

The objective of this study was to estimate the risk of thyroxine-treated AITD among patients with RA at different time points before and after the diagnosis of RA.

A nationwide register-based case-control and cohort study was conducted between January 1, 2006, and June 30, 2013, with a maximum follow-up time of 7 years before and 8 years after diagnosis of RA. The study used the Swedish Rheumatology Quality Register and linkage to other nationwide registers to identify 8090 adults with new-onset RA and a random population-based sample of 80 782 referents matched by age, sex, and residential area. Statistical analysis was performed from July 1, 2015, to June 30, 2017.

Presence of AITD in the participants in the case-control design and RA in the participants in the cohort design was evaluated. Prevalence and relative risk of incident AITD before (odds ratios) and after (hazard ratios) diagnosis of RA was compared with the population as reference.

Results: There were 8090 patients with RA and 80 782 population-based participants as reference who were identified. By the time of diagnosis of RA, the prevalence of AITD was 10.3% among the patients with RA vs 7.1% among the controls. This increased risk of AITD developed during the 5 years before diagnosis of RA and peaked by the time of diagnosis of RA. From diagnosis of RA and onward, the risk of developing AITD decreased.

Conclusively, Compared with the general population, Swedish patients with RA appear to have a higher prevalence of thyroxine-treated AITD at diagnosis of RA and an increased incidence of AITD during the 5-year period before diagnosis of RA. After diagnosis of RA, the risk of developing AITD is suggested to decrease below the expected rate. Besides temporal changes in diagnostic intensity, this pattern of risk raises the question whether AITD may influence the pathogenesis of RA (or vice versa) and, conversely, the question whether antirheumatic therapies may prevent AITD.

Source: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2707426