Thyroid Research Thyroid Research Archive Hyperthyroidism

Sonography may be useful in evaluating patients with amiodarone-induced hyperthyroidism

(July 2002)

The background of the study. Amiodarone is an iodine-rich antiarrhythmic drug that can cause hyperthyroidism, which may be due to iodine excess or to thyroiditis. This case study evaluated the role of color-flow Doppler ultrasonography for distinguishing between the two types of hyperthyroidism and the course of hyperthyroidism in untreated and treated patients.

How the study was done. The study subjects were 10 women and 27 men (mean age, 65 years) found to have amiodarone-associated hyperthyroidism at one large hospital from 1998 to 2000. Thyroid size was determined by two-dimensional ultrasonography, and thyroid vascularity by color-flow Doppler ultrasonography. Iodine-associated hyperthyroidism was diagnosed if the patient's thyroid gland was enlarged; thyroiditis-associated hyperthyroidism was diagnosed if the size was normal and vascularity was normal, patchy, or reduced.

The results of the study. The hyperthyroidism subsided spontaneously in seven patients. Based on the results of ultrasonography in five of the patients, two were thought to have iodine-induced hyperthyroidism and one thyroiditis-associated hyperthyroidism; the results were equivocal in two.

Thirty patients were treated for hyperthyroidism, of whom 25 underwent ultrasonography. Ten were considered to have iodine-associated hyperthyroidism and 10 thyroiditis-associated hyperthyroidism; the results were equivocal in 5. Among these 30 patients, 18 initially received an antithyroid drug (carbimazole) and prednisolone and 12 carbimazole alone. Amiodarone was discontinued in 26 patients. Twenty-five patients ultimately became euthyroid two required thyroidectomy); the other five patients died. The duration of hyperthyroidism and of treatment, and the total doses of carbimazole were similar in the patients with the two types of hyperthyroidism, but the total dose of prednisolone was lower in the patients with iodine-associated hyperthyroidism. No patient had recurrent hyperthyroidism after the cessation of therapy.

The conclusions of the study. Color-flow Doppler ultrasonography can help to distinguish between iodine excess and thyroiditis as the cause of hyperthyroidism in patients treated with amiodarone. It therefore may potentially allow more specific therapy.

The original article. Eaton SE, Euinton HA, Newman CM, Weetman AP, Bennet WM. Clinical experience of amiodarone-induced thyrotoxicosis over a 3-year period: role of colour-flow Doppler sonography. Clin Endocrinol 2002;56:33-8.