The effect of iodine administration on the development of thyroid autoimmunity in patients with nontoxic goiter

Previous studies, mostly performed in iodine-deficient areas, have suggested that the administration of iodine to patients with endemic goiter may be associated with the development of thyroid autoantibodies (ThAbs); however, this has not been a consistent finding. In this study, we evaluated the effect of iodine on thyroid function and on the development of indices of autoimmunity (ThAbs and lymphocytic infiltration) in an iodine replete area.

Iodized oil (1 mL) was administered intramuscularly to 40 euthyroid patients with nontoxic goiter, adequate iodine intake, and absent or normal levels of ThAbs. Blood and urinary samples were taken at time 0, 3, 6, and 12 months after iodine administration. Thyroid volume was evaluated and fine-needle aspiration (FNA) was performed at 0, 6, and 12 months.

Seven patients developed abnormal levels of ThAbs at some time between 3 and 12 months after iodine administration (p = 0.017). Mean anti-thyroglobulin (Tg) antibody levels increased at 6 months without reaching abnormal levels, but did not reach statistical significance (p = 0.062). Lymphocytic infiltration was detected in FNA smears in 10 cases before and in 27 cases after treatment (p = 0.0003). Triiodothyronine (T3) decreased at 12 months of follow-up, while thyroxine (T4) and thyrotropin (TSH) levels did not change significantly. A decrease in the mean levels of thyroglobulin as well as a small reduction in goiter size was observed at 6 and 12 months.

The administration of iodized oil to patients with small nontoxic goiter in an iodine-replete area was accompanied by the development of abnormal levels of ThAbs in some cases and by an increase in thyroid lymphocytic infiltration.