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

Objectives: Radioactive iodine ((131)I) 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 (131)I 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 (131)I, predictors of poor treatment response.

Results: Thirty-eight of 102 patients with persistent hyperthyroidism (37%) received (131)I (160 μCi/g thyroid tissue/(131)I 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 (131)I, 89% and 11% became hypothyroid after one and two (131)I doses, respectively. The goal of (131)I therapy was attainment of hypothyroidism. 'Poor treatment response' (seen in 27%) was defined as requirement for a second (131)I 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 (131)I (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 (131)I are achievable. Use of antithyroid drugs, pre-existing eye disease and prolonged time to (131)I may confer relative resistance to (131)I.