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

Background: Metaiodobenzylguanidine (MIBG) labeled with radioisotopes can be used for diagnostics ¹²³I⁻) and treatment (¹³¹I⁻) in patients with neuroblastic tumors. Thyroid dysfunction has been reported in 52% of neuroblastoma (NBL) survivors after ¹³¹I-MIBG, despite thyroid protection. Diagnostic ¹²³I-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 ¹²³I-MIBG only. Methods: Thyroid function and uptake of ¹²³I⁻ in the thyroid gland after ¹²³I-MIBG administrations were evaluated in 48 neuroblastic tumor survivors who had not been treated with ¹³¹I-MIBG. All patients had received thyroid prophylaxis consisting of potassium iodide or a combination of potassium iodide, thiamazole and thyroxine during exposure to ¹²³I-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 ¹²³I⁻ uptake was visible in the thyroid. In 1 patient with thyroid dysfunction, weak uptake of ¹²³I⁻ 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 ¹²³I-MIBG combined with thyroid protection. Randomized controlled trials are required to investigate whether administration of ¹²³I-MIBG without thyroid protection is harmful to the thyroid gland.