Thyroid Peroxidase Antibodies in Non-Autoimmune Hyperthyroidism Treated with Radioactive Iodine

Introduction: Earlier studies suggest increased serum levels of thyroid peroxidase antibodies (TPOAb) in some cases with non-autoimmune hyperthyroidism. The aim of the study was to assess the incidence of hypothyroidism in patients with nodular toxic goitre and toxic adenoma at 12 months after radioactive iodine therapy in the relation to TPOAb levels. Patients & Measurements: The study comprised 100 patients (83 females; 17 males) treated with radioactive iodine therapy. Serum concentrations of thyrotropin, free thyroxin, TPOAb, and anti-TSH receptor antibodies were assessed at baseline and 12 months after radioactive iodine therapy. Results: High TPOAb level (>60.0 IU/mL) was found in 27% of patients at baseline and 32% at the follow-up. Baseline TPOAb values were higher in subjects with coexisting non-thyroid autoimmune disease (p=0.041). After radioactive iodine therapy, the mean TPOAb level increased in patients with normal baseline TPOAb (p=0.03) and the rates of euthyroidism and hypothyroidism were 61 and 34%, respectively. The rate of hypothyroidism after radioactive iodine therapy was not significantly different in groups with normal and high baseline TPOAb. Conclusions: 27% of patients with non-autoimmune hyperthyroidism were positive for TPOAb. However, baseline TPOAb level did not influence the rate of hypothyroidism at 12 months after radioactive iodine therapy. Our results suggest a more close surveillance after radioactive iodine therapy of patients harboring these antibodies.