ABSTRACT
BACKGROUND/AIM: The aims of the study are to compare characteristics of subacute thyroiditis (SAT) related to different aetiologies, and to identify predictors of recurrence of SAT and incident hypothyroidism. METHODS: This nationwide multicenter retrospective cohort study included 53 endocrinology centers in Turkey. The study participants were divided into either coronavirus disease-2019 (COVID-19)-related SAT (Cov-SAT), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine-related SAT (Vac-SAT), or control SAT (Cont-SAT). RESULTS: Of the 811 patients, 258 (31·8%) were included in the Vac-SAT group, 98 (12·1%) in the Cov-SAT group, and 455 (56·1%) in the Cont-SAT group. No difference was found between the groups with regard to laboratory and imaging findings. The aetiology of SAT was not an independent predictor of recurrence or hypothyroidism. In the entire cohort, steroid therapy requirement and younger age were statistically significant predictors for SAT recurrence. C-reactive protein (CRP) measured during SAT onset, female gender, absence of anti-thyroid peroxidase (TPO) positivity, and absence of steroid therapy were statistically significant predictors of incident (early) hypothyroidism, irrespective of SAT aetiology. On the other hand, probable predictors of established hypothyroidism differed from that of incident hypothyroidism. CONCLUSION: Since there is no difference in terms of follow-up parameters and outcomes, COVID-19- and SARS-CoV-2- vaccine related SATs can be treated and followed up like classical SATs. The recurrence was determined by the younger age and steroid therapy requirement. Steroid therapy independently predict incident hypothyroidism that may sometimes be transient in overall SATs and is also associated with lower risk of established hypothyroidism.