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Ultrasound in Patients with Amiodarone Induced Thyrotoxicosis

Since amiodarone became available in the United States for anti-arrhythmic therapy in the 1980s, there have been numerous reports of associated changes in thyroid hormone metabolism, as well as clinically significant thyroid dysfunction. Amiodarone is a benzofuranic-derivative iodine-rich drug and is structurally similar to thyroxine. 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). Also, mixed forms characterized by coexistence of theese two phenomena exist. The identification of two main subtypes of AIT and of the respective pathogenic mechanisms provides the basis for a rational approach to medical treatment. Color-Flow Doppler Sonography (CFDS) provides real-time display of thyroid vascularity. The study by Bogazzi found all patients with type II AIT to have CFDS 0 or absent vascularity , whereas type I AIT patients had CFDS I to III, indicating increased vascularity of the gland. Italian authors evaluated separately parenchymal blood flow from that of nodules. The autors from Brasil , in very recent study , evaluated the usefulness of Doppler parameters in the differentiation between the two types of AIT. They measured: systolic peak velocity in the superior and inferior thyroid arteries, pulsatility index in the both thyroid arteries ; resistance index in the both arteries and color pixel density (CPD) of the thyroid parenchyma. Conclusions: CFDS can distinguish between type I and type II AIT, but is not always concordant with the thyroid RAIU. Separate evaluation of parenchymal blood flow from that of nodules may prove beneficial in the diagnosis of underlying thyroid diseases in patients with type 1 AIT. Objective tests such as systolic peak velocities in the thyroid arteries and CPD are reliable parameters for differentiating between the two types of AIT.

amiodarone; thyrotoxycosis; ultrasound

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