FRI461 Two-years Course Of Subacute Thyroiditis After COVID-19 Vaccination: A Case Report

Disclosure: S. Yoshida: None. COVID-19 has been reported to cause subacute thyroiditis. Furthermore, the literature includes cases of COVID-19 vaccine-related subacute thyroiditis, but few reports describe the long-term course of vaccine-induced subacute thyroiditis. Herein, we report the case of a 47-year-old woman with no medical history who developed subacute thyroiditis after mRNA COVID-19 vaccination and was followed up for 2 years. Her fever persisted after the second dose of the COVID-19 vaccine, and she became aware of left anterior neck pain 8 days later. There were no infectious disease symptoms or signs in the patient’s history or at a recent physical examination. All thyroid autoantibodies were negative. On ultrasound, the thyroid gland was diffusely enlarged, and internal echogenicity was diffusely hypoechoic, coarse, and color Doppler blood flow signals were decreased without confinement to the pain area. She was diagnosed with subacute thyroiditis with tender thyroid swelling, thyrotoxicosis, and an inflammatory reaction. It was suspected that there was a causal link between the onset of subacute thyroiditis and COVID-19 mRNA vaccination because it developed immediately after vaccination and there were no other obvious causes. She was started on prednisolone, and her symptoms improved rapidly, leading to hypothyroidism 1 month later. The swelling of the thyroid gland improved rapidly, and it became atrophic several months after the onset of subacute thyroiditis. She never received any additional vaccinations. Two years after the onset, there was no recurrence of subacute thyroiditis, thyroid atrophy persisted, and the patient required levothyroxine supplementation (100 µg/day). Subacute thyroiditis generally has a good prognosis and rarely leads to permanent hypothyroidism. Subacute thyroiditis due to vaccination may follow a different course than that due to typical viral infection, and we need to examine its long-term prognosis. Presentation: Friday, June 16, 2023