[Study of the long-term effects of amiodarone on thyroid function using ultrasensitive TSH measurements. Preliminary report].

The results of a prospective study of basal ultrasensitive TSH concentrations in patients during long-term treatment over 12 months with amiodarone are reported. 2 patients (3%) developed hypothyroidism, whereas no case of hyperthyroidism was observed. A significant increase in FT4 with a simultaneous decrease in T3 was demonstrated at every periodic investigation during amiodarone therapy. In most patients ultrasensitive TSH values stayed within the normal range and showed no significant alteration during treatment. A slow decline in TSH during therapy was observed in a subgroup of patients with completely euthyroid initial TSH concentrations. This TSH decrease reached statistical significance after 12 months' therapy. FT4 showed pathological results in 35% of all determinations at any time during the study, T3 in 27%, and TSH in only 17%. In conclusion, a new steady-state of thyroid tests is attained during treatment with amiodarone and most patients maintain a euthyroid function state. Assessment of ultrasensitive TSH can be recommended as a primary screening test for evaluation of thyroid function in patients under amiodarone therapy.