We evaluated whether thyroid function test (TFT) screening is warranted for patients with autoimmune rheumatic diseases (ARD) by comparing the incidence of hypothyroidism requiring treatment (HRT) in ARD patients and healthy controls (HCs). Medical records of 2307 ARD patients and 78,251 HCs for whom thyroid-stimulating hormone (TSH) levels were measured between 2004 and 2018 were retrospectively reviewed. Cumulative incidence of HRT in ARD patients and HCs was compared. HRT development was evaluated with age- and sex-adjusted Kaplan-Meier curve. Risk factors were identified with Cox proportional hazard models. HRT was significantly more common in ARD patients than in HCs (6.3% vs. 1.9%, P < 0.001). After adjusting for age, sex, and baseline TSH level, hazard ratios for HRT were significantly higher in overall ARD patients (hazard ratio [95% confidence interval] 3.99 [3.27-4.87]; P < 0.001), particularly with rheumatoid arthritis and antinuclear antibody-associated diseases in female, and antinuclear antibody-associated diseases, spondyloarthritis, and vasculitis in male patients. Baseline high TSH level, thyroid-related autoantibody positivity, high IgG, and renal impairment were significant risk factors for hypothyroidism development in ARD patients; 20% of high-risk patients developed HRT during follow-up. HRT was significantly more frequent in ARD patients. Careful TFT screening and follow-up could help detecting clinically important hypothyroidism.
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