Thyroid function after diagnostic (123)I-metaiodobenzylguanidine in children with neuroblastic tumors

BACKGROUND: Metaiodobenzylguanidine (MIBG) labeled with radioisotopes can be used for diagnostics (123)I(−)) and treatment ((131)I(−)) in patients with neuroblastic tumors. Thyroid dysfunction has been reported in 52% of neuroblastoma (NBL) survivors after (131)I-MIBG, despite thyroid protection. Diagnostic (123)I-MIBG is not considered to be hazardous for thyroid function; however, this has never been investigated. Therefore, the aim of this study was to evaluate the prevalence of thyroid dysfunction in survivors of a neuroblastic tumor who received diagnostic (123)I-MIBG only. METHODS: Thyroid function and uptake of (123)I(−) in the thyroid gland after (123)I-MIBG administrations were evaluated in 48 neuroblastic tumor survivors who had not been treated with (131)I-MIBG. All patients had received thyroid prophylaxis consisting of potassium iodide or a combination of potassium iodide, thiamazole and thyroxine during exposure to (123)I-MIBG. RESULTS: After a median follow-up of 6.6 years, thyroid function was normal in 46 of 48 survivors (95.8%). Two survivors [prevalence 4.2% (95% CI 1.2–14.0)] had mild thyroid dysfunction. In 29.2% of the patients and 11.1% of images (123)I(−) uptake was visible in the thyroid. In 1 patient with thyroid dysfunction, weak uptake of (123)I(−) was seen on 1 of 10 images. CONCLUSIONS: The prevalence of thyroid dysfunction does not seem to be increased in patients with neuroblastic tumors who received (123)I-MIBG combined with thyroid protection. Randomized controlled trials are required to investigate whether administration of (123)I-MIBG without thyroid protection is harmful to the thyroid gland.