Introduction Only about 30% of pediatric patients with Graves' hyperthyroidism achieve remission with medical therapy, and therefore radioactive iodine (RAI) therapy is often used as a definitive treatment. Although the goal of RAI is permanent hypothyroidism, this is not consistently achieved. We conducted a chart review to determine the factors associated with the success of RAI. We also tried to determine optimal follow-up post RAI and if there was an optimal L-thyroxine dose that would normalize the hypothyroid state quickly. Methods This is a retrospective chart review of Graves' patients who underwent RAI between 2008 and 2017. We included age, sex, time from diagnosis, thyroid gland size, total dose of I-131 and dose in μCi/g of thyroid tissue. Patients were grouped based on outcome and analyzed using univariate and multivariate logistic regression. Follow-up thyroid levels post RAI and after starting l-thyroxine were analyzed. Results There were 78 ablations including six repeat ablations. Seventy-three percent became hypothyroid, 23% remained overtly or subclinically hyperthyroid, and 4% were euthyroid. Smaller thyroid size (36.5 vs. 47.4 g; p = 0.037) and higher dose of I-131 (242 vs. 212 μCi/g thyroid tissue; p = 0.013) were associated with a higher likelihood of hypothyroidism. Most patients remained hyperthyroid at 1 month post RAI, but by 3 months the majority became hypothyroid. There was no clear L-thyroxine dose that normalized hypothyroidism quickly. Conclusions An I-131 dose close to 250 μCi/g of thyroid tissue has a higher likelihood of achieving hypothyroidism. Testing at 2-3 months after RAI is most helpful to confirm response to RAI.
Keywords: Graves’ disease; children; hyperthyroidism; radioiodine ablation.