Amiodarone-induced Thyrotoxicosis — EECC MCQ

Correct answer: C — Amiodarone-induced thyrotoxicosis (AIT) is the most likely cause if the patient is on amiodarone — it occurs in 3-5% of amiodarone-treated patients and requires differentiation into Type 1 (iodine-induced) vs Type 2 (destructive thyroiditis) for appropriate management

Amiodarone (which contains 37% iodine by weight) causes thyroid dysfunction in 15-20% of patients: hypothyroidism (more common in iodine-sufficient areas like the UK) and thyrotoxicosis (AIT, more common in iodine-deficient areas). AIT is classified as: Type 1 (excess iodine-induced thyroid hormone synthesis in pre-existing thyroid disease — treated with thionamides + perchlorate); Type 2 (destructive thyroiditis releasing preformed hormone — treated with corticosteroids). Mixed forms exist. AIT in HF is particularly dangerous as thyrotoxicosis increases cardiac output, heart rate, and oxygen demand, worsening HF and triggering AF. Amiodarone may need to be stopped (though its extremely long half-life means effects persist for months). Thyroidectomy may be needed for refractory AIT.

Reference: ESC (2024): AF Guidelines; ETA/ATA Amiodarone Thyroid Guidelines