BACKGROUND
Amiodarone is a medication used to manage difficult-totreat irregular heart rhythms (arrhythmias). Amiodarone can cause various types of thyroid problems, including thyrotoxicosis, a condition of high thyroid hormone levels. Amiodarone-induced thyrotoxicosis (AIT) can be difficult to treat because there are two different types that need different treatments. Type 1 AIT is caused by high iodine content of amiodarone, a main component of thyroid hormone, leading to excess production of thyroid hormone by the thyroid gland. Type 2 AIT is caused by inflammation of the thyroid gland from amiodarone, leading to release of excess amount of preformed and stored thyroid hormone from the thyroid gland. Type 1 AIT is treated with antithyroid drugs to stop thyroid hormone production. Type 2 AIT is treated with steroid to decrease inflammation.

Thyrotoxicosis can cause rapid or irregular heart rhythms. Since patients who are treated with amiodarone have underlying heart disease, it is important to quickly control thyrotoxicosis in these patients to minimize its impact on heart. Because diagnosis may not be always clear, there may be delay in diagnosis and starting appropriate treatment for AIT. This study examined whether the initial treatment received by patients with AIT affects cardiovascular outcomes.

THE FULL ARTICLE TITLE
Cappellani D et al 2023 Real-life data on the effect of medical therapy for amiodarone-induced thyrotoxicosis on CV events and hospitalizations. J Clin Endocrinol Metab 108:1298–1307. PMID: 36585895.

SUMMARY OF THE STUDY
A total of 313 patients with AIT who were referred to and treated at the University of Pisa in Italy between January 1997 and May 2020 were included in the study. Information from their medical records were used.

Patients were divided into two groups based on initial treatment received before they were seen at the University of Pisa Endocrine specialty clinic: appropriate therapy group if they received appropriate treatment for the type of AIT, and inappropriate therapy group if they received no treatment or the wrong treatment for the type of AIT. Outcomes compared between two groups included duration of thyrotoxicosis, and frequencies of heart problems (including arrhythmia, congestive heart failure, heart attack and stroke), hospitalization, and urgent thyroid surgeries performed to control thyrotoxicosis.

Among 313 patients, 108 patients received appropriate therapy and 205 received inappropriate therapy. Patients in the inappropriate therapy group had longer duration of thyrotoxicosis. Patients in the inappropriate therapy group had more heart events compared to those in the appropriate therapy group (33% vs 5%). In addition, patients in the inappropriate therapy group had more hospitalizations and urgent thyroid surgeries compared to those in the appropriate therapy group (25% vs 7% for hospitalization, and 7% vs 2% for urgent thyroid surgeries). Side effects from the treatment were minimal and similar between two groups.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The authors concluded that in patients with amiodaroneinduced thyrotoxicosis, starting appropriate treatment quickly decreases duration of thyrotoxicosis and risks of adverse heart events, hospitalization, and urgent thyroid surgeries. This study shows that it is important to accurately diagnose the type of AIT. Distinguishing two types of AIT can be confusing at times. If the type of AIT is not clear, starting treatment for both types of AIT with continued re-evaluation may be indicated to minimize risks of heart problems in patients.

— Sun Y. Lee, MD, MSc

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