Similar age-dependent levothyroxine requirements of schoolchildren with congenital or acquired hypothyroidism.

UNLABELLED: A recent study in children suggested that levothyroxine requirements are higher in congenital than in acquired hypothyroidism but did not match for severity of disease. Here, we studied only children with congenital or acquired hypothyroidism who had an undetectable fT4 at diagnosis. There were eight girls with congenital hypothyroidism due to athyreosis and eight girls with acquired hypothyroidism due to autoimmune thyroid disease. The median levothyroxine dose received at the most recent visit when serum TSH was <5.0 mU/L (at a median age of 7.86 and 14.29 years, respectively) was 3.2 mcg/kg/day in the former and 2.4 mcg/kg/day in the latter (N.S.). Combining both groups, the levothyroxine requirement decreased by 0.5 mcg/kg/day for every 4-year period. CONCLUSION: When strictly matched for severity of disease, levothyroxine requirements are similar in school-age children with congenital or acquired hypothyroidism and decrease with age. Thus, in congenital hypothyroidism treated early with high-dose levothyroxine, pituitary resistance to thyroxine feedback does not appear to be present at school age. WHAT IS KNOWN: • Pediatric studies unmatched for severity have suggested that levothyroxine requirements are higher in congenital than in acquired hypothyroidism. What is new: • When strictly matched for severity, levothyroxine requirements are similar in children with congenital or acquired hypothyroidism and decrease with age.