The role of ¹²³I imaging in the evaluation of infants with mild congenital hypothyroidism

Background/Aims: Controversy exists regarding the diagnosis and treatment of mild congenital hypothyroidism (MCH). We studied the value of ¹²³I imaging in patients with MCH. Methods: Retrospective chart review of infants and children <4 years of age who underwent ¹²³I imaging: group 1 = MCH [thyroid-stimulating hormone (TSH) <25 μIU/ml, normal free T₄/T₃], group 2 = severe congenital hypothyroidism (TSH ≥25 μIU/ml), and group 3 = MCH in infancy imaged after treatment withdrawal at age 3 years. Data collected included 4- and 24-hour ¹²³I uptake, TSH, free T₄/total T₃ at imaging, age at imaging, and levothyroxine (L-T₄) dose at 1 year of. Results: Thirty-six patients underwent ¹²³I imaging. In group 1 (n = 20, median TSH: 8.49 μIU/ml), 85% had abnormal imaging consistent with dyshormonogenesis. Two patients were referred after 1 year of age. The median age at imaging for the remaining 18 patients was 54 days. Median L-T₄ dose at 1 year of age for these 18 patients was 2.8 μg/kg, which is consistent with dyshormonogenesis. Ninety-one percent of group 2 (n = 11, median TSH: 428.03 μIU/ml) had abnormal imaging. The median age at imaging was 13 days. Four patients in group 3 had abnormal ¹²³I imaging and restarted treatment. Conclusion:¹²³I imaging is a valuable tool for evaluation, diagnosis, and treatment of MCH.