Incidence and timing of thyroid dysfunction with long term amiodarone therapy.

The aim of this retrospective study was to assess the incidence, timing and classical presentations of thyroid dysfunction in patients treated long-te rm with amiodarone. Ninety patients (sex ratio M/W 67/33, mean age 71 years) were followed up f or 48 months. The daily dose of amiodarone was 200 mg after loading doses d uring the hospital stay for atrial fibrillation. The average treatment peri od was 33 +/- 19 months. Hypothyroidism, observed in 5.5% of cases, occurred at variable intervals w ith few clinical manifestations. Hyperthyroidism was more common (12.2%), o ccurred increasingly with time, and was clinically symptomatic with recurre nt supraventricular arrhythmias in 36% of cases. Long-term amiodarone therapy causes undesirable thyroid side-effects for ne arly 1 out of 3 patients. Hyperthyroidism is more common than hypothyroidis m and may be explained by increased iodine intake. The increasing incidence of hyperthyroidism with time suggests a cumulated dose relationship, a sit uation which is not observed with hypothyroidism.