Thyrotropin receptor antibodies and graves' disease, a side-effect of 131I treatment in patients with nontoxic goiter

The use of 131I treatment in patients with benign nontoxic goiter is increasing, and the described side-effects are few. In this paper we describe appearance of TSH receptor antibodies (TRAb) and concomitant development of hyperthyroidism as a side-effect of 131I treatment in patients with nontoxic goiter. In this retrospective study, 191 consecutive patients with 131I-treated nontoxic goiter are described. Nine patients (5%) developed hyperthyroidism 3 months after 131I treatment, and 5 patients (3%) developed radiation thyroiditis within the first month. Frozen sera were analyzed for thyroid peroxidase antibodies (anti-TPO) in 130 patients before 131I treatment. In 21% of these, serum levels of anti-TPO were over 200 U/mL. The complication frequency of Graves'-like hyperthyroidism and hypothyroidism was 51% in patients with elevated anti-TPO (n = 27) and 15% in patients with normal serum anti-TPO levels (P < 0.00005). TRAb, anti-TPO, and thyroglobulin were followed in patients developing hyperthyroidism or radiation thyroiditis and in 10 control patients remaining euthyroid. At the time of 131I treatment, all patients had serum TRAb values within the normal range. Three months after administration of 131I, the patients developing hyperthyroidism had a transient extensive rise in serum TRAb and anti-TPO levels parallel to a rise in the serum free T4 index. In patients developing radiation thyroiditis, serum TRAb values were normal. In control patients, serum TRAb and anti-TPO values were both within the normal range throughout the observation period. In conclusion, hyperthyroidism can be triggered by 131I in patients with nontoxic goiter, not only related to radiation thyroiditis but also as a Graves'-like hyperthyroidism induced by TRAb. Elevated anti-TPO pretreatment is a marker of an increased risk of side-effects to 131I treatment in nontoxic goiter.