[Incidence and timing of thyroid dysfunction with long-term amiodarone therapy]. / Incidence et délai d'apparition des dysthyroïdies sous traitement chronique par amiodarone.

The aim of this retrospective study was to assess the incidence, timing and classical presentations of thyroid dysfunction in patients treated long-term with amiodarone. Ninety patients (sex ratio M/W 67/33, mean age 71 years) were followed up for 48 months. The daily dose of amiodarone was 200 mg after loading doses during the hospital stay for atrial fibrillation. The average treatment period was 33 +/- 19 months. Hypothyroidism, observed in 5.5% of cases, occurred at variable intervals with few clinical manifestations. Hyperthyroidism was more common (12.2%), occurred increasingly with time, and was clinically symptomatic with recurrent supraventricular arrhythmias in 36% of cases. Long-term amiodarone therapy causes undesirable thyroid side-effects for nearly 1 out of 5 patients. Hyperthyroidism is more common than hypothyroidism and may be explained by increased iodine intake. The increasing incidence of hyperthyroidism with time suggests a cumulated dose relationship, a situation which is not observed with hypothyroidism.