Amiodarone-induced thyroid dysfunction in a tertiary center in south Brazil

Abstract

Amiodarone, used in the treatment of cardiac arrhythmias, is associated with thyroid dysfunction. No reports exist on its frequency in southern Brazil, nor studies evaluating the usefulness of clinical scores to diagnose thyroid abnormalities in these patients. This study aimed at determining the prevalence of amiodarone-induced thyroid dysfunction in a representative sample from a tertiary center, to study the conditions associated to this dysfunction and to evaluate the reliability of clinical scores of hypo and hyperthyroidism. One hundred ninety-five amiodarone users were submitted to a clinical and laboratory evaluation. Of these, 2.1% were hyperthyroid, 25.1% hypothyroid and 9.2% had only a high T4. Considering thyroid dysfunction variables researched, thyroid autoimmunity was positively associated (OR 4.8; p= 0.02), and male gender had a trend to a positive association (OR 1.86; p= 0.06). Clinical scores were highly sensitive for hyperthyroidism (100%), but not for hypothyroidism (8%). The low prevalence of amiodarone-induced hypothyroidism suggests that this specific region is iodine-sufficient. All patients receiving chronic amiodarone therapy should be checked for clinical scores for hyperthyroidism and laboratory evaluation should be performed, as a screening for thyroid dysfunction, especially if they are male or have positive microsomal antibodies.

How frequently should a patient taking amiodarone be screened for thyroid dysfunction?

“…Our results agree with reports that could not find a relationship between AITD and dosage or duration of amiodarone treatment (4,7,8,12,13). We also could not demonstrate that a baseline cardiac condition such as Chagas' disease was associated with AITD.…”

Incidence of amiodarone-induced thyroid dysfunction and predictive factors for their occurrence

“…These figures are similar to the ave-rage up-to-date reported incidence of clinical dysfunctions and in accordance with data on more frequent occurrence of AIH in the regions having sufficient iodine supply [4,8]. Sixteen percent of patients developed clinical thyroid dysfunction, while 21% developed some form of sub-clinical dysfunction.…”

“…According to some reports, AIH occurs early during amiodarone treatment [3]. The incidence of amiodarone-induced thyrotoxicosis (AIT), reported up to date, is 0.003%-23%, most frequently 1%-5% [4,5,7]. AIT is more frequent in areas of low iodine ingestion by food and in men [6].…”

Incidence and predictability of amiodarone-induced thyrotoxicosis and hypothyroidism

“…A slight and usually transient increase in serum thyrotropin (TSH) is therefore frequently observed in the first 3-4 months of therapy [6]. Incidence rates of the more severe amiodarone-induced thyrotoxicosis (AIT) and amiodarone-induced hypothyroidism (AIH) are described as being dissimilar, ranging from < 1% to 23% and 47%, respectively [7][8][9][10][11][12][13][14][15][16]. Despite these effects on thyroid hormone metabolism, many patients do not show changes in thyroid function during longterm intake of amiodarone.…”