A Case of Amiodarone-Induced Thyrotoxicosis Presenting With Methimazole-Induced Agranulocytosis

Amiodarone is a class III anti-arrhythmic drug found to be effective in treating multiple life-threatening arrhythmias, including paroxysmal atrial fibrillation. Despite its effectiveness, amiodarone has been found to result in thyroid dysfunction. Amiodarone-induced thyrotoxicosis (AIT) is classified as type 1, which often develops in those with autoimmune hyperthyroid conditions, or type 2, which occurs because of destructive thyroiditis in an apparently normal thyroid. Differentiating between both types often poses a clinical and therapeutic dilemma, as AIT 1 is treated with thionamides, whereas AIT 2 requires steroids for treatment. We present a case of a patient with AIT who was treated empirically for both subtypes with methimazole and prednisone without clinical improvement. Methimazole was later stopped due to concern for agranulocytosis, and the patient was then treated with cholestyramine, metoprolol, and prednisone. Given persistent thyrotoxicosis, the decision was made to proceed with surgical intervention. The patient underwent a successful total thyroidectomy without complications. The patient's condition clinically improved post-surgery and was discharged home on post-operative day 2 in stable condition. Prednisone was tapered over two weeks, and he was started on a weight-based dose of levothyroxine. He continues to follow up in our clinic for postoperative hypothyroidism and is clinically and biochemically euthyroid.