Subacute Thyroiditis during the SARS-CoV-2 Pandemic

Context: Acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been related to subacute thyroiditis (SAT). Objective: We compared SAT cases during the SARS-CoV-2 pandemic to those observed in the previous years. Methods: A cross-sectional, retrospective study was conducted at the Endocrinology Unit of University Hospital of Pisa, Italy. We included all patients observed from January 2016 to December 2020 because of an untreated SAT, who had developed the disease within 15 days prior to the visit. SAT cases from 2016 to 2019 (N=152) are referred to as pre-SARS-CoV-2, while 2020 SAT patients are classified as pos-SARS-CoV-2 (N=18) or neg-SARS-CoV-2 (N=28), according to positive or negative SARS-CoV-2 testing performed up to 45 days from SAT onset. Results: While during 2016-2019, most SAT cases were observed in the third quarter, in 2020, 2 peaks were seen, superimposable to the SARS-CoV-2 outbreaks in the second and the fourth quarters. In the second and fourth quarters of 2020, we observed higher levels of free thyroxine (FT4), C-reactive protein (CRP), and thyroglobulin (Tg) compared with the same quarters of the years 2016-2019. Pos-SARS-CoV-2 patients had higher FT4 (28.4 vs 24.1 nmol/L), CRP (8.5 vs 3.6 mg/L), and Tg (155 vs 60 μg/L) (P0.05 for all) and more frequently had hypothyroidism (13/15 vs 30/152 at 3 months) (P0.001) than pre-SARS-CoV-2 patients. Neg-SARS-CoV-2 patients showed a clinical picture intermediate between the other 2 groups. Conclusion: The SARS-CoV-2 pandemic has caused a shift in the annual timing and severity of SAT cases.