Use of Radioactive Iodine in Type 2 Amiodarone-Induced Thyrotoxicosis

Amiodarone-induced thyrotoxicosis (AIT) is a well-recognized etiology of hyperthyroidism. A case is reported here which demonstrates that radioactive iodine ablation therapy (RAI) can be used to treat type 2 AIT, even at lower radioactive iodine uptake (RAIU) levels than what conventional teaching would recommend for RAI.

An 80-year-old male with atrial fibrillation and cardiomyopathy was found to have type 2 AIT. He was refractory to other treatments for atrial fibrillation and therefore dependent on amiodarone. He was started on prednisone to treat AIT but developed fluid overload. As he was deemed a poor surgical candidate for thyroidectomy, recombinant human thyroid-stimulating hormone-stimulated RAI was administered with 29.5-mCi I-131; he subsequently developed subclinical hypothyroidism despite pre-RAI RAIU of 3%. He remained on amiodarone until he received a heart valve replacement, which temporarily relieved the atrial fibrillation and allowed for amiodarone discontinuation. After atrial fibrillation recurred and in anticipation of resuming amiodarone, he received a second dose of recombinant human thyroid-stimulating hormone-stimulated RAI at 26.5 mCi I-131, which rendered him clinically hypothyroid.

RAI therapy can be considered as a potential treatment strategy for type 2 AIT if the RAIU is at least 3%.

This case demonstrates that RAI is an effective treatment strategy for type 2 AIT if the patient cannot tolerate steroids and is not a candidate for thyroidectomy. This case also illustrates how RAI can be used to prevent AIT.