Amiodarone-Induced Thyrotoxicosis
A 45-year-old man with atrial fibrillation started on amiodarone 6 months ago. TFTs now show TSH <0.01 mU/L, elevated FT4 and FT3. He has no goitre and normal inflammatory markers. Which subtype of amiodarone-induced thyrotoxicosis is most likely, and what is the most appropriate first-line treatment?
Correct Answer — B
Type 2 AIT is a destructive thyroiditis — amiodarone directly damages follicular cells, causing passive release of preformed thyroid hormone. It occurs in a structurally normal gland and shows low/absent vascularity on Doppler USS. No goitre here confirms a normal gland. First-line treatment is prednisolone, which targets the underlying inflammatory-destructive process. Type 1 AIT occurs in a pre-existing abnormal gland (nodular goitre or latent Graves') and requires carbimazole ± perchlorate.
Key concept
AIT Type 1 (iodine-induced, abnormal gland) → carbimazole ± perchlorate. AIT Type 2 (destructive, normal gland) → prednisolone.