Background: Subacute thyroiditis is a clinical condition usually seen 1-2 weeks after a viral infection in the upper respiratory tract, and has also been reported following infection with COVID-19. Cases of subacute thyroiditis following a seasonal influenza vaccination have been described, and recent case reports have reported clinical symptoms and signs typical of subacute thyroiditis following vaccination with mRNA SARS-CoV-2 vaccine.
Case presentation: A young, healthy female underwent surgery with left-side lobectomy for papillary thyroid carcinoma. Hashimoto's thyroiditis was revealed as an additional histological finding. Six days prior to complementary thyroidectomy of the right lobe the patient received mRNA SARS-CoV-2 vaccine. The histological slides showed features consistent with extensive subacute thyroiditis throughout the entire lobe.
Interpretation: As no other aetiology could account for the subacute thyroiditis, the vaccination against COVID-19 is seen as a plausible source.