Expansion
Type 1 is excess synthesis; type 2 is destructive thyroiditis
Expansion
Amiodarone contains about 37 per cent iodine by weight, delivering an enormous iodine load, and it inhibits peripheral T4 to T3 conversion. It has a half-life of about 50 days, so effects persist long after stopping.
Hypothyroidism is commoner in iodine-replete areas: the thyroid fails to escape the Wolff-Chaikoff effect. Treated with thyroxine, and amiodarone can usually be continued.
Thyrotoxicosis comes in two forms:
| Type 1 | Type 2 | |
|---|---|---|
| Mechanism | Iodine-induced excess synthesis (Jod-Basedow) | Destructive thyroiditis with release of stored hormone |
| Underlying gland | Abnormal (nodular or latent Graves) | Normal |
| Doppler vascularity | Increased | Decreased |
| Treatment | Carbimazole | Prednisolone |
Mixed forms occur, and it is often not possible to distinguish them, so both treatments are given together.
Amiodarone also causes a characteristic pattern in euthyroid patients: T4 and reverse T3 rise, T3 falls, and TSH rises transiently then normalises.