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

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

Automated summary

The prevalence of thyroid dysfunction does not seem to be increased in patients with neuroblastic tumors who received I-123-MIBG combined with thyroid protection.