Management of amiodarone-induced thyrotoxicosis

Amiodarone is used increasingly in a number of cardiac conditions. Amiodarone is heavily iodinated and can cause thyroid dysfunction. The diagnosis of amiodarone-induced thyrotoxicosis remains difficult and more common causes of thyrotoxicosis need to be considered and excluded. Amiodarone has a significant side effect profile, which includes thyroid dysfunction. Amiodarone is an effective drug and its withdrawal may have significant impact on a patient's already fragile cardiac status. There are three different types of amiodarone-induced thyrotoxicosis (AIT) (I, II and mixed). Identification of the different subtypes of AIT allows a rational and appropriate management strategy to be chosen. Type I occurs in patients with underlying thyroid disease, whilst type II is thought to result from a destructive thyroiditis. Differentiation is based on clinical grounds together with investigations, which can include thyroid function test, radioiodine uptake scanning, measurement of interleukin-6 levels and colour flow Doppler sonography. Amiodarone should be discontinued in both types of AIT if the indication for its use is not a life-threatening cardiac condition. The management of type I centres around antithyroid drugs to control thyrotoxicosis and later consideration of more definitive treatment. Type II AIT responds to steroid therapy, although antithyroid drugs may be useful if symptoms are severe. Therapeutic options for refractory cases of AIT include surgery, radioiodine and plasmapheresis.