How should we be treating children with congenital hypothyroidism?

Early detection by newborn screening and appropriate L-thyroxine treatment leads to normal or near-normal neurocognitive outcome in infants with congenital hypothyroidism. Many newborns with congenital hypothyroidism have some residual thyroid hormone production, and even in those with athyreosis, transplacental passage of maternal thyroid hormone offers some protection for a time. Given the serum T4 half-life of 6 days, the neonatal T4 level will fall and disappear over the first 2-3 weeks of life. Thus, there is a crucial 'window of opportunity' to correct the hypothyroidism and minimize the time the brain is exposed to hypothyroxinemia. While there are few truly prospective, randomized clinical trials investigating treatment parameters, studies measuring IQ outcome support a starting L-thyroxine dose of 10-15 microg/kg/day. Further, studies show that the most severely hypothyroid infants are at risk for a 5-20 point decrease in IQ. Such infants may benefit from a starting dose of 12-17 microg/kg/d, which has been shown to normalize T4 in 3 days and TSH in 2 weeks. Target serum T4 or free T4 levels appear to be higher in the first two weeks of treatment. Infants require more frequent laboratory monitoring, every 1-2 months in the first 6 months and every 3-4 months until age 3 years, as the developing brain has a critical dependence on thyroid hormone in the first 2-3 years of life.