A 58-year-old man on amiodarone for atrial fibrillation develops thyrotoxicosis. Which mechanism of amiodarone-induced thyroid dysfunction is characterized by absent vascularity on color Doppler ultrasound?
- A Type 1: Iodine-excess driven autonomous hormone synthesis with increased vascularity
- B Autoimmune Graves' disease induced by iodine load with high vascularity
- C Type 2: Amiodarone causes destructive thyroiditis with release of preformed thyroid hormones; thyroid is avascular due to inflammatory destruction ✓
- D TSH-secreting pituitary adenoma with hyperplastic thyroid
Explanation
Amiodarone-induced thyrotoxicosis (AIT) has two main types. Type 1 (iodine-excess driven, usually in patients with pre-existing nodular goiter) shows increased vascularity on Doppler as hormone synthesis is elevated. Type 2 is a destructive thyroiditis caused by direct amiodarone toxicity to follicular cells, releasing preformed thyroid hormones; because the gland is damaged and not hyperfunctioning, vascularity is absent or very low on color Doppler (avascular pattern). Type 2 is treated with corticosteroids, whereas Type 1 responds to thionamides and potassium perchlorate.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.