ABSTRACT
BACKGROUND: COVID-19 is known to cause an acute respiratory illness, although clinical manifestations outside of the respiratory tract may occur. Early reports have identified SARS-CoV-2 as a cause of subacute thyroiditis (SAT). METHODS: A systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. MEDLINE, Web of Science and PubMed databases were queried in February 2021 for studies from December 2019 to February 2021. MeSH search terms 'COVID-19', 'SARS-CoV-2' and 'coronavirus' along with search terms 'thyroiditis', 'thyrotoxicosis' and 'thyroid' were used. Descriptive statistics for continuous variables and proportions for categorical variables were calculated. RESULTS: Fifteen publications reporting on 17 individual cases of COVID-19-induced SAT were identified. Age ranged from 18 to 69 years. The majority (14 of 17; 82%) of cases were female. The delay between onset of respiratory symptoms and diagnosis of SAT ranged from 5 to 49 days (mean, 26.5). Systemic inflammatory response syndrome related to viral infection was uncommonly reported at the time of SAT diagnosis. Thyroid ultrasonography frequently reported an enlarged hypoechoic thyroid with decreased vascularity and heterogenous echotexture. Elevated C-reactive protein (CRP) was common at the time of SAT diagnosis, with results ranging from 4.5 to 176 mg/L (mean, 41 mg/L). Antithyroid antibodies were frequently negative. SAT-specific treatment included corticosteroids for 12 of 17 (70.5%) patients. Most returned to normal thyroid status. CONCLUSION: COVID-19-associated SAT may be difficult to identify in a timely manner due to potential absence of classic symptoms, as well as cross-over of common clinical features between COVID-19 and thyrotoxicosis.