Abstract

Congenital hypothyroidism (CH), if not correctly treated with L-thyroxine (L-T4), may be responsible for a permanent intellectual disability.If patients treated with L-T4 do not achieve a good TSH control, the possibility of poor compliance and/or poor absorption of L- T4 shouldbe investigated. We describe an infant with CH whose thyroid hormone levels worsened after she started a carob-bean gum thickenedformula. A baby girl was diagnosed with CH by newborn screening (at confirmatory blood evaluation TSH was 496.0 μIU/mL and FT4 0.13ng/dl). Five weeks after beginning L-T4 treatment TSH normalized (TSH 2.72 μIU/mL, FT4 2.08 ng/dl); nevertheless, only another 5 weekslater we noticed a new worsening of thyroid hormone levels (TSH 31.1 μIU/mL, FT4 1.27 ng/dl), which worsened further (TSH 44.8μIU/mL, FT4 1.16 ng/dl) even if L-T4 dosage was increased. Anamnesis disclosed that she had been given a carob-bean gum thickenedformula to combat gastroesophageal reflux disease (GERD) rather than regular type 1 formula milk. The anti-reflux milk formula wasdiscontinued and after 14 days the patient’s TSH level dropped to 0.38 μIU/mL and FT4 increased to 2.68 ng/dL, allowing the L-T4 dosage tobe reduced. Carob-bean gum thickened formula may influence the absorption of L-T4. If such formulas are used, we recommend a morefrequent evaluation of thyroid function. In CH infants, inexplicably high TSH levels could be caused by gastrointestinal disorders or theinterference of drugs or other substances, including some types of milk formula, which impair L-T4 absorption.