A 56-year-old man on amiodarone for atrial fibrillation develops thyrotoxicosis: TSH less than 0.01 mIU/L, free T4 3.2 ng/dL, free T3 6.5 pg/mL. Examination reveals a small diffuse goitre, and anti-TPO antibodies are positive. Colour Doppler of the thyroid shows markedly increased vascularity. Which is the most appropriate treatment?
- A Prednisolone 40 mg daily as monotherapy
- B Radioactive iodine ablation
- C Carbimazole combined with perchlorate ✓
- D Total thyroidectomy only if drug therapy fails immediately
Correct answer: C. Carbimazole combined with perchlorate
Explanation
Increased Doppler vascularity, a goitre, and positive TPO antibodies identify amiodarone-induced thyrotoxicosis type 1, an iodine-induced form on a background of latent autoimmune disease. It responds to thionamides, often with perchlorate to block further iodine uptake. Prednisolone alone treats type 2 destructive thyroiditis, which shows absent Doppler flow. Radioiodine fails because iodine saturation prevents uptake.
Reference: Williams Textbook of Endocrinology, 14th ed.
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Written and medically reviewed by the StethoPrep medical team.