Unexpected Onset of Severe Hypothyroidism Following a Thyroid Technetium Scan in a Young Patient With Graves' Disease: A Case Report.

This is a case report of a 20-year-old Bahraini man who presented for a regular check-up. Upon further questioning, he complained of difficulty gaining weight. Initial laboratory results indicated Graves' disease (thyroid-stimulating hormone (TSH), 0.02 mIU/L; free T4, 29 pmol/L), which was confirmed by homogeneous diffuse uptake on thyroid scintigraphy. Shortly after the iodine-based scan, the patient developed tremors, palpitations, and dizziness. A thyroid function test (TFT) revealed an abrupt transition to severe hypothyroidism (TSH, 141.76 mIU/L; free T4, 3.3 pmol/L). This shift could be explained by iodine-induced thyroid dysfunction in the context of underlying autoimmunity or other possible mechanisms, such as the Wolff‒Chaikoff effect, iodine-induced thyroiditis, or autoimmune switching leading to biochemical hypothyroidism. The article addresses a rare phenomenon and highlights the need for careful monitoring after iodine-based imaging in patients with autoimmune thyroid disease.