A Rare Side Effect of Vaccine-Induced Thyrotoxicosis: A Case Report.

Graves' disease is an autoimmune thyroid disorder driven by thyroid-stimulating hormone receptor antibodies (TRAb), resulting in hyperthyroidism. Autoimmune thyroid dysfunction has increasingly been reported following SARS-CoV-2 infection and, more recently, in association with COVID-19 vaccination. This case highlights a potential link between the ChAdOx1 nCoV-19 (AstraZeneca) vaccine and new-onset Graves' disease. A 49-year-old man presented with a two-week history of palpitations, weight loss, diarrhea, and dyspnea. Symptoms began approximately two weeks after his second dose of the AstraZeneca COVID-19 vaccine. He had no prior thyroid history but had a background of Crohn's disease in remission. Examination revealed tachycardia and a diffusely enlarged, non-tender thyroid gland. Laboratory findings demonstrated suppressed TSH (<0.01 mU/L), markedly elevated free thyroxine (>100 pmol/L), and raised TRAb (9.56 IU/L). Thyroid ultrasound showed diffusely enlarged lobes with heterogeneous echotexture and increased vascularity, consistent with Graves' disease. The patient was treated with carbimazole, propranolol, and corticosteroids, with gradual clinical and biochemical improvement. At one-year follow-up, he remained euthyroid with TRAb levels reduced to 1.25 IU/L and no relapse of symptoms. Clinicians should consider vaccine-associated autoimmune thyroid disease in patients presenting with hyperthyroid symptoms shortly after COVID-19 vaccination. Early recognition, confirmation through TRAb testing, and appropriate management are critical. Long-term follow-up is essential to monitor for relapse or remission in post-vaccination Graves' disease.