Subacute thyroiditis: clinical significance of diffuse 18-fluorodeoxyglucose uptake. Case report

Background. Subacute thyroiditis is a rare inflammatory thyroid disease presumably associated with viral infection, including COVID-19. It accounts for about 5% of all thyroid diseases. Materials and methods. A clinical case of de Quervain's subacute thyroiditis in a patient with diffuse hypermetabolic 18-fluorodeoxyglucose uptake by the thyroid gland is presented. Results. A 61-year-old patient with no history of thyroid disorders 3 weeks after COVID-19 experienced fever in the evenings (37.839.8C). He had moderate pain in the thyroid gland with radiation to the jaw, severe weakness, hand tremors, shivers, 12 kg weight loss, and sweating. These symptoms lasted for 3 weeks. Physical examination showed an enlarged thyroid gland, dense and extremely tender, especially its left lobe. Ultrasound showed an enlarged thyroid gland with a heterogeneous structure and large hypoechoic areas in both lobes up to 47 mm with fuzzy contour. Color Doppler imaging revealed reduced blood flow. Combined positron-emission and X-ray computed tomography with 18-fluorodeoxyglucose showed an increased diffuse uptake of the radiopharmaceutical in the thyroid gland and enlargement of its lobes, SUVmax 10.55. Blood thyroid-stimulating hormone is low, free triiodothyronine and thyroxine are high, and ferritin concentration is markedly increased, consistent with thyrotoxicosis. A fine-needle aspiration biopsy was performed. Cytology confirmed de Quervain's subacute thyroiditis. Glucocorticoids and nonsteroidal anti-inflammatory drugs were administered. Four weeks after the treatment, the clinical manifestations resolved. The patient was assessed in 6 months. Ultrasound showed a thyroid gland of regular size with smooth contours; color Doppler mapping revealed normal blood flow. Thyroid-stimulating hormone, triiodothyronine, and thyroxine were within reference ranges. Conclusion. The SARS-CoV-2 virus can be regarded as the cause of subacute thyroiditis. Combined positron-emission and X-ray computed tomography with 18-fluorodeoxyglucose showed diffuse intensive radiopharmaceutical uptake in the thyroid gland. Cytology is the basis for differential diagnostics. Glucocorticoids and nonsteroidal anti-inflammatory drugs are the first-choice agents.