[Thyroid functional parameters during anti-arrhythmia therapy with amiodarone]

Thyroid function was investigated in 41 patients on chronic treatment with amiodarone. 27% of the patients had elevated total thyroxine levels together with elevated free thyroxine levels. Thyrotropin (TSH) secretion was completely suppressed in 15% of the patients. Elevated free or total thyroxine levels were frequently observed together with normal TSH secretion, although 5 of the 6 patients with suppressed TSH had markedly elevated levels. Triiodothyronine (T3) levels were low normal or below the normal range in all patients but one. This was the only patient who apparently developed amiodarone-induced hyperthyroidism. The clinical symptoms of this patient were equivocal. Thyroid function parameters including T3 levels returned to normal only 3 months after withdrawal of the drug. The patient did not need any thyrostatic treatment. The duration of treatment with amiodarone did not influence thyroid hormone concentrations, although there was an insignificant trend of increasing total thyroxine levels after a year of treatment. There was, moreover, no significant influence of the dose (200-500 mg orally/day) of amiodarone on thyroid hormone levels. Our results show that the usual screening parameters of thyroid function, namely total and free thyroxine serum concentrations, are not reliable in patients on chronic amiodarone treatment. The incidence of amiodarone-induced hypothyroidism was 2.4%. We did not observe an amiodarone-induced hypothyroidism, although there was one patient with increased TSH levels but normal T3 and thyroxine levels.