Long-Term Outcomes of Radioiodine Therapy for Juvenile Graves Disease with Emphasis on Subsequently Detected Thyroid Nodules: A Single Institution Experience from Japan.

Objective: To investigate the long-term outcomes of radioiodine therapy (RIT) for juvenile Graves disease (GD) and the ultrasonographic changes of the thyroid gland.

Methods: All of 117 juvenile patients (25 males and 92 females, aged 10 to 18 [median 16] years) who had undergone RIT for GD at our clinic between 1999 and 2018 were retrospectively reviewed. Each RIT session was delivered on an outpatient basis. The maximum I dose per treatment was 13.0 mCi, and the total I dose per patient was 3.6 to 29.8 mCi (median, 13.0 mCi). I administration was performed once in 89 patients, twice in 26, and three times in 2 patients. Ultrasonography of the thyroid gland was regularly performed after RIT. The duration of follow-up after the initial RIT ranged from 4 to 226 (median 95) months.

Results: At the latest follow-up more than 12 months after RIT (n = 111), the patients' thyroid functions were overt hypothyroidism (91%), subclinical hypothyroidism (2%), normal (5%), or subclinical hyperthyroidism (2%). New thyroid nodules were detected in 9 patients, 4 to 17 years after initial RIT. Patients with newly detected thyroid nodules underwent RIT with lower doses of I and had larger residual thyroid volumes than those without nodules. None of the patients were diagnosed with thyroid cancer or other malignancies during the follow-up period.

Conclusion: Over a median follow-up period of 95 months (range, 4 to 226 months), RIT was found to be effective and safe in juvenile GD. However, cumulative evidence from further studies is required to confirm the long-term safety of RIT for juvenile GD.

Abbreviations: ATD = antithyroid drug; GD = Graves disease; KI = potassium iodide; LT4 = levothyroxine; MMI = methimazole; PTU = propylthiouracil; RAIU = radio-active iodine uptake; RIT = radioiodine therapy; Tc = technetium-99m; TSH = thyrotropin.