Amiodarone-induced thyroid dysfunction in an iodine-replete area: epidemiological and clinical data

The present study aims to evaluate the incidence, types, timing and risk factors in amiodarone (AMD)-induced thyroid dysfunction.

The study comprised 229 patients from an iodine-replete area (115 women, 114 men, mean age 63.8 ± 9.2 years), chronically treated with AMD. The cases were clinically investigated prior to, and during treatment, by thyroid 2D and color Doppler flow sonography, thyroid function tests (TSH, FT3, FT4), and antithyroid antibodies.

Of 88 patients (38.4%) who developed thyroid dysfunction, 47 (20.5%) presented AMD-induced thyrotoxicosis (AIT) and 41 (17.9%) AMD-induced hypothyroidism (AIH). There is an evident prevalence of subclinical AIH (29 cases), compared to subclinical AIT (three cases). Regarding clinical forms, these prevailed in AIT (44 patients) (p 〈 0.001, Fisher's exact test). Thyrotoxic patients were classified in pathogenic types as follows: 11 cases as type 1, 15 cases as type 2, and 21 cases as mixed form. The most important risk factor for the development of thyroid dysfunction was represented by the underlying thyroid pathology. The patients with previous thyroid abnormalities (diffuse or nodular goitre and/or positive antithyroid antibodies) developed earlier thyroid dysfunction compared to those with an apparently normal thyroid gland. The thyroid dysfunction occurrence was heterogeneous (4-84 months). Thyrotoxicosis involved especially young ages, while AIH affected later years.The daily dose, the duration of the treatment and the cumulative dose of AMD do not represent risk factors in thyroid dysfunction development. The determination of serum AMD and desethylamiodarone concentrations does not offer benefits in the diagnosis and treatment of thyroid dysfunction.

In the present study, the incidence of AIH was similar to that reported in iodine-replete areas. The incidence of AIT was higher that previously reported, a fact underlining the importance of the proper screening and monitoring of patients. Cases with previous thyroid morphologic and/or immunologic abnormalities require frequent monitoring.