A 61-year-old man on amiodarone for atrial fibrillation develops thyrotoxicosis: free T4 3.4 ng/dL, TSH less than 0.01 mIU/L. The thyroid is small and multinodular without tenderness. Interleukin-6 is not elevated and colour Doppler shows increased parenchymal vascularity. Which statement is correct regarding his condition?
- A It is a destructive thyroiditis best treated with glucocorticoids
- B It results from iodine-induced hormone synthesis and responds to thionamides ✓
- C Radioactive iodine ablation is the treatment of first choice
- D Thyroid uptake scan will show diffusely increased tracer uptake
Correct answer: B. It results from iodine-induced hormone synthesis and responds to thionamides
Explanation
Amiodarone-induced thyrotoxicosis type 1 occurs in an abnormal thyroid (nodular goitre or occult Graves disease); the iodine load drives autonomous hormone synthesis. It shows preserved or increased Doppler flow and normal interleukin-6, and it responds to carbimazole or propylthiouracil. Type 2 is a destructive process with absent flow, raised interleukin-6 and steroid responsiveness. Radioactive iodine is ineffective because iodine saturation blocks uptake.
Reference: Williams Textbook of Endocrinology, 14th ed.
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