A 61-year-old man on long-term amiodarone develops weight loss, tremor, and atrial fibrillation with rapid ventricular rate. Free T4 is 3.4 ng/dL, free T3 mildly elevated, TSH suppressed. Colour-flow Doppler of the thyroid shows diffusely increased vascularity and the gland contains a small autonomous nodule. Which form of amiodarone-induced thyrotoxicosis does he have, and what is the preferred initial therapy?
- A Type 1, treat with potassium perchlorate alone
- B Type 2, treat with prednisolone
- C Type 1, treat with thionamides such as carbimazole ✓
- D Type 2, treat with radioiodine ablation
Correct answer: C. Type 1, treat with thionamides such as carbimazole
Explanation
Increased thyroid vascularity with a nodular gland indicates Type 1 AIT, where amiodarone's iodine load drives autonomous hormone synthesis in underlying thyroid autonomy; thionamides are first-line. Type 2 is a destructive thyroiditis with low vascularity on Doppler and responds to glucocorticoids. Radioiodine uptake is poor in both forms because of iodine saturation, making ablation ineffective acutely.
Reference: Williams Textbook of Endocrinology, 14th ed.
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Written and medically reviewed by the StethoPrep medical team.