engleski

Amiodarone: influence on thyroid function and morphology

Amiodarone is a benzofuranic derivative containing a large amount of iodine (37, 2 mg/100 mg of active drug), widely used in treatment of tachyarrhythmias. The average maintenance dose of amiodarone contains up to 1000 times daily iodine requirement. It is well known that excess of iodine intake may alter thyroid function , presented as amiodarone-induced hypothyroidism (AIH) or amiodarone-induced thyrotoxicosis (AIT). AIT may arise from iodine-induced excessive thyroid hormone synthesis (type I) or destructive thyroiditis with release of hormones (type II). The aim of this study was to evaluate impact of amiodarone on thyroid function and morphology. 48 patients on chronic amiodarone treatment (6 months - 2 years) were included in this study. The mean value of urinary iodine excretion was 423, 5 mg/L. 2h I-131 uptake mean value was 4, 2% (range 3, 1-5, 6%). There was no patient with elevated I-131 uptake. Hypothyreosis was found in 16% and hyperthyreosis in 28% of cases. T3/T4 ratio in euthyroid patients was 9, 7x103. Thyroid antibodies were positive in 60% of patients. Ultrasound revealed autoimmune thyroiditis in 46%, diffuse goiter in 19% and nodular goiter in 19% of cases. Normal US finding was found in 16%. Among 14 pts with hyperthyreosis Color Flow Doppler sonography (CFDS) was performed in 9 pts. In 8 pts CFDS demonstrated increased glandular vascularity, diagnostic for type I AIT, and only in one case vascularity was absent (type II AIT). High frequency of autoimmune thyroiditis in pts on chronic amiodarone therapy sugest important role of iodine excess in autoimmune processes. Amiodarone-induced thyrotoxycosis was more frequent finding then hypothyreoidism as was expected due to lower iodine intake in this area. Patients treated with amiodarone may manifest altered thyroid hormone profile without thyroid dysfunction (decreased T3/T4 ratio).

amiodarone; thyroid; ultrasound

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