A Case Report of Conversion from Hashimoto's Thyroiditis to Graves' Disease in Type 1 Diabetic Patient Following the COVID-19 Vaccination.

Background: A considerable number of COVID-19 vaccines became available following the outbreak. Yet, various inflammatory and autoimmune complications have been reported following vaccination. We aimed to report the case of a type 1 diabetic patient converting from Hashimoto's thyroiditis to Graves' disease after the fourth dose of COVID-19 vaccine, thought to trigger an autoimmune/inflammatory syndrome induced by adjuvants (ASIA syndrome).

Case Presentation: A thirty-one-year-old female patient with type 1 diabetes and Hashimoto's thyroiditis applied to our clinic with complaints of palpitations, anxiety, and weight loss one month after the fourth dose of COVID-19 vaccine (2 doses of CoronaVac + 2 doses of Pfizer/BioNTech). She was receiving levothyroxine 50 mcg/day. When her thyroid function tests showed thyrotoxicosis, we initially considered thyroxine-related exogenous thyrotoxicosis. However, we considered Graves' disease upon persisting thyrotoxicosis despite thyroxine withdrawal, positive serum TSH receptor antibody titers, and other imaging findings. Therefore, various autoimmune and inflammatory events have been reported after the COVID-19 vaccination. Adjuvants in vaccines can trigger autoimmune events, which lead to ASIA syndrome. COVID-19 vaccines may cause increased TSH receptor antibody levels or change the balance in the activity of blocking and stimulating antibodies, which may cause a conversion from Hashimoto's to Graves' disease.

Conclusion: This was the first case report where the patient experienced a conversion from Hashimoto's to Graves' disease after COVID-19 vaccination, which may ultimately be related to ASIA syndrome. Yet, more data is needed to elucidate such a relationship, and patients should closely be checked regularly after four doses of vaccination.