Approach to the patient with amiodarone-induced thyrotoxicosis.
Amiodarone, a benzofuranic iodine-rich antiarrhythmic drug, causes thyroid dysfunction in 15-20% of cases. Although amiodarone-induced hypothyroidism poses no particular problem, amiodarone-induced thyrotoxicosis (AIT) is a diagnostic and therapeutic challenge. There are two main forms of AIT: type 1, a form of iodine-induced hyperthyroidism, and type 2, a drug-induced destructive thyroiditis. However, mixed/indefinite forms exist that may be caused by both pathogenic mechanisms. Type 1 AIT usually occurs in abnormal thyroid glands, whereas type 2 AIT develops in apparently normal thyroid glands (or small goiters). Diagnosis of thyrotoxicosis is easy, based on the finding of increased free thyroid hormone concentrations and suppressed TSH levels. Thyroid radioactive iodine (RAI) uptake values are usually very low/suppressed in type 2 AIT, most commonly low or low-normal, but sometimes normal or increased in type 1 AIT despite the iodine load. Color flow Doppler sonography shows absent hypervascularity in type 2 and increased vascularity in type 1 AIT. Mixed/indefinite forms may have features of both AIT types. Thionamides represent the first-line treatment for type 1 AIT, but the iodine-replete gland is not very responsive; potassium perchlorate, by inhibiting thyroid iodine uptake, may increase the response to thionamides. Type 2 AIT is best treated by oral glucocorticoids. The response very much depends on the thyroid volume and the severity of thyrotoxicosis. Mixed/indefinite forms may require a combination of thionamides, potassium perchlorate, and steroids. RAI is usually not feasible in AIT due to low RAI uptake values. Thyroidectomy represents a valid option in cases resistant to medical therapy.
Bogazzi
Fausto
F
Department of Endocrinology, University of Pisa, Ospedale Cisanello, Via Paradisa, 2, 56124 Pisa, Italy.
Bartalena
Luigi
L
Martino
Enio
E
D000368:Aged; D000638:Amiodarone / Q000009:adverse effects* / Q000627:therapeutic use; D000889:Anti-Arrhythmia Agents / Q000009:adverse effects* / Q000627:therapeutic use; D001281:Atrial Fibrillation / Q000150:complications* / Q000188:drug therapy*; D015415:Biomarkers; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics; D008297:Male; D049268:Positron-Emission Tomography; D017256:Technetium Tc 99m Sestamibi; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000000981:diagnostic imaging; D013971:Thyrotoxicosis / Q000139:chemically induced* / Q000000981:diagnostic imaging / Q000628:therapy; D014463:Ultrasonography
D000889:Anti-Arrhythmia Agents; D015415:Biomarkers; D007457:Iodine Radioisotopes; D017256:Technetium Tc 99m Sestamibi; D000638:Amiodarone