Antithyroid drug therapy is effective in
many patients with amiodarone-induced hyperthyroidism
(July 2002)
The background
of the study. Amiodarone, a drug given to treat
patients with cardiac arrhythmias, can cause two types of hyperthyroidism,
one due to iodine excess and the other due to thyroiditis. This
study was done to determine if patients with either type of hyperthyroidism
respond to antithyroid drug therapy and the effect of the cessation
of amiodarone therapy on outcome.
How the study was done.
The study subjects were 4 women and 24 men (median age, 64 years)
with amiodarone-induced hyperthyroidism seen at the thyroid clinic
at a single teaching hospital. The diagnosis was based on a low
serum thyrotropin concentration and high serum free thyroxine and
free triiodothyronine concentrations. Patients with nodular goiter,
or diffuse goiter or other features of Graves' disease, were categorized
as having iodine-induced hyperthyroidism, and those with none of
these findings were categorized as having thyroiditis-induced hyperthyroidism.
The results of the study.
The indications for amiodarone therapy were ventricular tachycardia
in 14 patients and atrial arrhythmias in 14 patients. The most common
symptoms of hyperthyroidism were weight loss and worsening palpitations.
Amiodarone was continued in 17 patients, including 12 of the patients
with ventricular tachycardia.
In 5 patients, 4 of whom continued amiodarone, hyperthyroidism
resolved spontaneously in a median interval of 3 months. The other
23 patients were treated with carbimazole, and all became euthyroid
(median interval, 5 months). Three patients developed hypothyroidism
that persisted after carbimazole was stopped. The total dose of
carbimazole and the rate of improvement in thyroid function were
similar in the patients in whom amiodarone was stopped and those
in whom it was continued.
Fourteen patients were considered to have iodine-induced hyperthyroidism
and 12 patients thyroiditis-induced hyperthyroidism. There were
no differences between these two groups in the duration of amiodarone
therapy before the onset of hyperthyroidism, the cumulative dose
of amiodarone, or the cumulative dose of carbimazole needed to achieve
euthyroidism.
The conclusions of the study.
Among patients with amiodarone-induced hyperthyroidism, antithyroid
drug therapy is equally effective in those with iodine-induced and
those with thyroiditis-induced hyperthyroidism.
The original article.
Osman F, Franklyn JA, Sheppard MC, Gammage MD. Successful treatment
of amiodarone-induced thyrotoxicosis. Circulation 2002;105:1275-7.
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