The background of the study. Amiodarone, a drug given to treat patients with cardiac arrhythmias, can cause two types of hyperthyroidism, one due to iodine excess and the other due to thyroiditis. This study was done to determine if patients with either type of hyperthyroidism respond to antithyroid drug therapy and the effect of the cessation of amiodarone therapy on outcome.
How the study was done. The study subjects were 4 women and 24 men (median age, 64 years) with amiodarone-induced hyperthyroidism seen at the thyroid clinic at a single teaching hospital. The diagnosis was based on a low serum thyrotropin concentration and high serum free thyroxine and free triiodothyronine concentrations. Patients with nodular goiter, or diffuse goiter or other features of Graves' disease, were categorized as having iodine-induced hyperthyroidism, and those with none of these findings were categorized as having thyroiditis-induced hyperthyroidism.
The results of the study. The indications for amiodarone therapy were ventricular tachycardia in 14 patients and atrial arrhythmias in 14 patients. The most common symptoms of hyperthyroidism were weight loss and worsening palpitations. Amiodarone was continued in 17 patients, including 12 of the patients with ventricular tachycardia.
In 5 patients, 4 of whom continued amiodarone, hyperthyroidism resolved spontaneously in a median interval of 3 months. The other 23 patients were treated with carbimazole, and all became euthyroid (median interval, 5 months). Three patients developed hypothyroidism that persisted after carbimazole was stopped. The total dose of carbimazole and the rate of improvement in thyroid function were similar in the patients in whom amiodarone was stopped and those in whom it was continued.
Fourteen patients were considered to have iodine-induced hyperthyroidism and 12 patients thyroiditis-induced hyperthyroidism. There were no differences between these two groups in the duration of amiodarone therapy before the onset of hyperthyroidism, the cumulative dose of amiodarone, or the cumulative dose of carbimazole needed to achieve euthyroidism.
The conclusions of the study. Among patients with amiodarone-induced hyperthyroidism, antithyroid drug therapy is equally effective in those with iodine-induced and those with thyroiditis-induced hyperthyroidism.
The original article. Osman F, Franklyn JA, Sheppard MC, Gammage MD. Successful treatment of amiodarone-induced thyrotoxicosis. Circulation 2002;105:1275-7.