Radioactive iodine for hyperthyroidism in children and adolescents: referral rate and response to treatment

Objectives Radioactive iodine (¹³¹I) therapy is increasingly viewed as a safe and effective treatment for paediatric and adolescent hyperthyroidism. Our objective was to estimate treatment response and its predictors and describe current referral practices for ¹³¹I therapy. Design Retrospective study. Patients One hundred and thirty‐one children 30 days–21 years old with laboratory evidence of hyperthyroidism, seen in an academic paediatric and adolescent endocrinology practice. Measurements Rate of referral, indications for ¹³¹I, predictors of poor treatment response. Results Thirty‐eight of 102 patients with persistent hyperthyroidism (37%) received ¹³¹I (160 μCi/g thyroid tissue/¹³¹I uptake), as did an additional 10 patients initially evaluated by adult thyroidologists. Primary indications were intolerance to (29%) or poor control on (19%) antithyroid drugs, patient preference (50%) and unknown (2%). Of 48 patients treated with ¹³¹I, 89% and 11% became hypothyroid after one and two ¹³¹I doses, respectively. The goal of ¹³¹I therapy was attainment of hypothyroidism. ‘Poor treatment response’ (seen in 27%) was defined as requirement for a second ¹³¹I dose or failure to achieve hypothyroidism after 6 months. Predictors of poor treatment response included: previous use of antithyroid drugs (37%vs. 0%, P = 0·02), ophthalmopathy (58%vs. 8%, P = 0·002), and an interval of ≥12 months from diagnosis to ¹³¹I (50%vs. 10%, P = 0·003). A very elevated free T4 tended to be more prevalent in those with poor response. Conclusions In children and adolescents with hyperthyroidism, high rates of success after ¹³¹I are achievable. Use of antithyroid drugs, pre‐existing eye disease and prolonged time to ¹³¹I may confer relative resistance to ¹³¹I.