Ultrasound Appearance of Thyroid Tissue in Hypothyroid Infants

ObjectiveTo identify those infants who need a higher starting dose of levothyroxine (l-T4) for early normalization of thyroid-stimulating hormone (TSH) level.Study designTSH levels at 2 time points (1 to 3 weeks and 3 to 5 weeks) after l-T4 therapy at a starting dose of 8 to12 μg/kg/day were evaluated retrospectively in 22 hypothyroid infants screened for congenital hypothyroidism (CH) in terms of etiology as determined by ultrasonography (US), the size of distal femoral epiphysis (DFE), and initial thyroid function.ResultsThe infants with a noneutopic thyroid or small DFE exhibited significantly higher posttherapeutic TSH levels compared with the other infants. Eight of the 9 infants who failed to achieve normalized TSH values at 1 to 3 weeks had noneutopic thyroid. All of the infants with eutopic thyroid exhibited normalized TSH at 3 to 5 weeks, and a significantly greater proportion of the infants with eutopic thyroid exhibited normalized TSH at 1 to 3 weeks compared with those with noneutopic thyroid. Stepwise regression analysis demonstrated that US etiology was a significant independent variable for normalization of TSH at 1 to 3 weeks.ConclusionsUS examination to identify eutopic or noneutopic thyroid provides useful information for determining the starting dose of l-T4 in hypothyroid infants.