Amiodarone is an anti-arrhythmic drug used in the treatment of tachyarrhythmias, ischemic heart disease, and congestive heart failure. Because its structure can imitate thyroxine, it can interfere with thyroid metabolism. Amiodarone-induced thyrotoxicosis is classified into two subtypes which are distinguished based on: basic pathogenesis (whether or not there is an underlying thyroid abnormality present), the predominant histologic changes, and therapeutic intervention. Type II disease, also called destructive thyroiditis, arises in an otherwise normal thyroid gland.

The predominant histologic features include destruction of thyroid follicles with desquamated epithelial cells present, involutional changes, focal fibrosis, and collections of foamy macrophages. Glucocorticoids are typically used as treatment (as opposed to thioamides, which are used in the treatment of Type I disease where the underlying pathology is due to excess hormone production). Cessation of amiodarone treatment usually results in most patients with type II disease returning to a euthyroid state. In scenarios where amiodarone must be continued and medical control of thyrotoxicosis is not achievable, thyroidectomy is considered.

See related content for references:

1) Saad, A. et al. Arch Pathol Lab Med. 2004 Jul;128(7):807-10.