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.
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