Amiodarone-induced thyrotoxicosis following treatment for amiodarone-induced hypothyroidism

Amiodarone-induced thyroid dysfunction is common but the development of hyperthyroidism following treatment for amiodarone-induced hypothyroidism is very unusual. We recently saw an elderly man who developed severe thyrotoxicosis four years after diagnosis of and initiation of treatment for amiodarone-induced hypothyroidism. The thyrotoxicosis was treated first with methimazole and discontinuation of L-thyroxine replacement and then with methimazole and prednisone. After successful treatment and withdrawal of therapy, he subsequently re-developed hypothyroidism and required resumption of L-thyroxine replacement. This case highlights that amiodarone-induced hyperthyroidism can occur in patients who previously became hypothyroid on the drug.