[Amiodarone and thyroid function: clinical implications].

Abstract

World-wide, the incidence of amiodarone-induced thyroid dysfunction is estimated to be between 2% and 24%. More than 50% of patients who receive long-term amiodarone have abnormal results on thyroid function tests. However, most of these patients are euthyroid. In a euthyroid amiodarone-treated patient, an increase in serum thyroxine levels (total and free) and in serum reverse T3 levels and a decrease in serum T3 levels (total and free), are observed. TSH levels are within the normal range with chronic treatment (more than 3 months). The aim of this study was to identify the frequency of amiodarone prescription by cardiologists, to learn about their clinical practice in screening for thyroid dysfunction, and to formulate guidelines for clinical investigation of thyroid function before and during amiodarone treatment. A questionnaire was sent to 27 cardiologists in private practice in the Geneva area and to 12 cardiologists in Geneva University Hospital (19 and 7 questionnaires returned respectively). Cardiologists in private practice prescribe amiodarone quite frequently (once to twice per month and more). Clinical investigation prior to treatment involves history (95%), clinical examination (63%) or thyroid function tests (37% routinely, 16% where there is clinical suspicion of thyroid dysfunction). Thyroid function is investigated by determination of TSH (100%), free T4 (68%), free T3 (50%), total T3 (32%) or total T4 (26%). Antithyroid antibodies are measured only by 10% of the cardiologists in private practice. Cardiologists would restrict amiodarone prescription in cases of clinical hyperthyroidism (90%), clinical hypothyroidism (74%), in the presence of goitre in a hyper- or hypothyroid patient (79 and 63% respectively), and if antithyroid antibodies were positive (32%). During amiodarone treatment 84% of cardiologists in private practice repeat thyroid function tests occasionally and 16% only in the presence of clinical signs. Hypothyroidism is a reason for withdrawing amiodarone treatment for 58% of the cardiologists and 37% would prescribe substitution. Hyperthyroidism is a reason for immediately suspending treatment for 90% of the cardiologists, only 5% would continue and 16% would prescribe antithyroid drugs. In conclusion, there is considerable divergence of opinion among cardiologists concerning investigation and interpretation of thyroid function before and during amiodarone treatment. Simple and practicable guidelines are needed.