thyrotoxicosis (AIT). The excess iodine from the amiodarone provides increased substrate, resulting in enhanced thyroid hormone synthesis and hyperthyroidism. (See 'Type I' above.) Destructive thyroiditis (type II AIT) typically occurs in patients with no underlying thyroid disease. (See 'Type II' above.) In iodine-sufficient areas, amiodarone-induced hypothyroidism appears to be more common than hyperthyroidism. In contrast, amiodarone-induced hyperthyroidism (usually type I AIT) is more common than hypothyroidism in iodine-deficient regions. (See 'Dietary iodine intake' above.) We suggest continuing amiodarone therapy in patients who develop amiodarone-induced hypothyroidism (Grade 2C). (See 'Treatment' above.) The diagnosis and treatment of amiodarone-induced hypothyroidism is the same as for other patients with primary hypothyroidism. Euthyroidism should be restored by replacement with thyroid hormone. Thyroid hormone, in doses larger than normal, is often required. (See 'Treatment' above.) Amiodarone should only be discontinued if it fails to control the underlying arrhythmia. If amiodarone is discontinued in a patient without preexisting autoimmune thyroid disease, the hypothyroidism often resolves. (See 'Treatment' above.) There are two types of AIT. In type I, there is increased synthesis of thyroid hormone (excess iodine provides the increased substrate), whereas in type II, there is excess release of T4 and T3 due to a destructive thyroiditis (direct toxic effect of amiodarone on the thyroid gland). For patients with type II AIT, the hyperthyroid phase may last from several weeks to several months and is often followed by a hypothyroid phase and then recovery. (See 'Types of hyperthyroidism' above.) https://www.uptodate.com/contents/amiodarone-and-thyroid-dysfunction/print 13/19 7/5/23, 8:17 AM Amiodarone and thyroid dysfunction - UpToDate It is often difficult to distinguish between the two types, and some patients may have elements of both. The 24-hour radioiodine uptake is typically not able to distinguish between types I and II AIT, because the high levels of ingested iodine with amiodarone results in 24-hour uptakes of less than 1 percent in most patients with either type I or type II AIT. Technetium-99m (99mTc)-sestamibi imaging, where available, or color-flow Doppler sonography (CFDS) may be the best ways of distinguishing between the two types of AIT. (See 'Differentiating the two types' above.) In patients who develop AIT in whom the amiodarone was prescribed for life-threatening ventricular arrhythmias (and is effective), we suggest continuing the amiodarone and simultaneously treating the hyperthyroidism (Grade 2C). (See 'Should amiodarone be discontinued?' above.) In patients who develop AIT in whom the amiodarone was not prescribed for life- threatening ventricular arrhythmias (or is ineffective), we suggest discontinuing the drug (Grade 2C). This should only be done in consultation with the patient's cardiologist if alternative antiarrhythmics can be used. For type I AIT, amiodarone should not be discontinued until hyperthyroid symptoms are well controlled with thionamides, since worsening hyperthyroid symptoms due to increased T3 levels may occur when the amiodarone is discontinued. (See 'Should amiodarone be discontinued?' above.) For the treatment of type I AIT, we suggest thionamides as our first choice of therapy (whether amiodarone is continued or discontinued) (Grade 2B) (see 'Thionamides' above). Although radioiodine ablation has been reported to have been used (in rare patients with high enough radioiodine uptake), this is usually not an option due to low radioiodine uptake in the majority of type I patients. (See 'Radioiodine' above.) Higher than average initial doses of thionamides are usually needed (30 to 40 mg of methimazole or 450 to 600 mg propylthiouracil [PTU] daily). Perchlorate or lithium are sometimes added to speed recovery, however, perchlorate is not available in the United States. In addition, perchlorate has been associated, albeit rarely, with aplastic anemia. (See 'Thionamides' above.) For the treatment of type II AIT, we suggest glucocorticoid therapy as our first-line drug (whether amiodarone is continued or discontinued) (Grade 2B). We typically start with prednisone (40 to 60 mg/day) and continue therapy for one to two months before tapering (to avoid exacerbations of hyperthyroidism). (See 'Glucocorticoids' above.) Patients with type I or type II AIT who are refractory to medical therapy should be treated by thyroidectomy. When balancing the risk of a surgical procedure during careful https://www.uptodate.com/contents/amiodarone-and-thyroid-dysfunction/print 14/19 7/5/23, 8:17 AM Amiodarone and thyroid dysfunction - UpToDate cardiovascular monitoring with the risk of several months of unmonitored and uncontrolled thyrotoxicosis, the advantages of surgery in this setting become compelling. (See 'Surgery' above and 'Surgery' above.) If the mechanism of the hyperthyroidism is uncertain or the patient appears to have "mixed" type I and type II AIT, a combination of prednisone (40 mg/day) and methimazole (40 mg/day) is reasonable initial therapy. A rapid response suggests type II AIT; the methimazole can then be tapered or stopped. A poor or slow initial response argues for type I AIT. (See 'Treatment if mechanism unknown' above.) Use of UpToDate is subject to the Terms of Use. REFERENCES 1. 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David S Cooper, MD No relevant financial relationship(s) with ineligible companies to disclose. Jean E Mulder, MD No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/amiodarone-and-thyroid-dysfunction/print 19/19