Clinical characteristics of amiodarone-induced thyrotoxicosis and hypothyroidism in Japan

Since amiodarone was introduced in Japan in 1992, the incidence of the drug -induced thyroid dysfunction has been increasing. We studied the thyroid fu nction of 13 patients with amiodarone-induced thyrotoxicosis (AIT) and 11 p atients with amiodarone-associated hypothyroidism (AAH) who had been referr ed to our Institute in the last 6 years. AIT and AAH developed after 39+/-2 1 and 20+/-16 months of amiodarone treatment, respectively. One patient dev eloped AAH followed by AIT. The AIT ranged from subclinical to overt thyrot oxicosis. Four patients with moderate to marked AIT were treated with methi mazole. Their thyrotoxicosis persisted for 3 to 9 months, despite administr ation of antithyroid agents. One patient with mild thyrotoxicosis was treat ed with prednisolone, resulting in a euthyroid state in a few months. Eight patients with asymptomatic to moderate thyrotoxicosis resolved spontaneous ly without any treatment. In four asymptomatic patients with AIT, serum lev els of T-3 and T-4 were in the upper normal range or slightly high (<12 mu g/dl), accompanied by suppressed TSH (<0.1 mu U/ml) and high thyroglobulin levels, suggesting destruction-induced thyrotoxicosis. Such a subclinical t hyrotoxicosis developed repeatedly in one patient. Ultrasonographic studies revealed no nodular lesion in the thyroid, and color flow Doppler sonograp hy demonstrated no hypervascularity in the thyroid gland in any AIT patient . Although it is postulated in Europe that there are two types of AIT, name ly type I, which develops in patients with latent Graves' disease or toxic multinodular goiter, and type II, which develops in an apparently normal th yroid as destructive thyroiditis, all AIT patients we have seen so far had developed destructive type AIT. Sufficient intake of iodide and a very low incidence of toxic multinodular goiter may account for the rare incidence o f type I AIT in our country. Mild to moderate AIT resolved spontaneously wi thout discontinuing amiodarone, but it was discontinued in two of 13 AIT pa tients because of extrathyroidal adverse reactions.