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

The use of I-131 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 I-131 treatment in patients with nontoxic goiter. In this retrospective study, 191 consecutive patients with I-131-treated nontoxic goiter are described. Nine patients (5%) developed hyperthyroidism 3 months after I-131 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 I-131 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 I-131 treatment, all patients had serum TRAb values within the normal range. Three months after administration of I-131, th, patients developing hyperthyroidism had a transient extensive rise in serum TRAb and anti TPO levels parallel to a rise in the serum free T-4 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 I-131 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 I-131 treatment in nontoxic goiter.