MON-269 Analysis of Clinical Features of Congenital Hypothyroidism with Eutopic Thyroid Gland

Background: Newborn screening test for congenital hypothyroidism (CH) may detect mild forms of CH, associated with eutopic thyroid gland, but there is no clear provision of the management. We analyzed the clinical features of CH with eutopic thyroid gland and necessity of continuation of treatment. Materials and methods: Retrospective, single center cohort study of children with CH treated between 2002 and 2018. CH patients initiating levothyoxin (LT4) within 2 months of age and reaching 3 years of age at the analysis were eligible. Aged >3 years CH patients with LT4 administration underwent re-evaluation test, which included thyroid function testing after LT4 therapy withdrawal, scan of thyroid using ultrasonography and computed tomography, and (123)I thyroid scintigraphy with potassium thiocyanate discharge test. The forms of CH were classified as thyroid dysgenesis or dyshormogensis, and the necessity of treatment were classified as permanent CH (PCH) or transient CH (TCH). PCH was defined when the subject was kept on administration of LT4 at the final observation. TCH was defined when a trial-off therapy was successful for at least 6 months. Developmental analysis and genetic analysis were performed in selected cases. Results: Of 209 CH patients, 103 cases were excluded from this study mainly because of age less than 3 years, incomplete medical records and lost to follow-up. 106 cases eligible for this study and 12 cases discontinued LT4 administration before 3 years of age without re-evaluation test. 94 cases underwent re-evaluation test, 69 cases had PCH and 25 cases had TCH. Median of final observation point for PCH was 12.0 years. In the PCH group, thyroid dysgenesis was the most prevalence form (31 had eutopic thyroid gland and 19 had ectopic thyroid gland or agenesis), 5 cases had dyshormogenesis and 14 cases were unclassifiable. All TCH patient had eutopic thyroid gland. PCH patients with eutopic thyroid gland had higher mean dose of LT4 at 3 years old than patients with TCH (2.27 µg/kg/day vs 1.39 µg/kg/day, p<0.01), but no other clinical features and developmental test results differed. LT4 dose at 3 years of age < 1.60 µg/kg/day was a predictive factor of TCH; sensitivity 78.2% and specificity 94.7%. Conclusion: PCH patients with eutopic thyroid gland presents a difference of LT4 dose at 3 years of age compared with TCH, and TCH is strongly suggested when the dose of LT4 is less than 1.60 µg/kg/day.