Worsening of Congenital Hypothyroidism After Start of Carob-bean Gum Thickened Formula: Is There a Link? A Case Report.

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 should be investigated. We describe an infant with CH whose thyroid hormone levels worsened after she started a carob-bean gum thickened formula. A baby girl was diagnosed with CH by newborn screening (at confirmatory blood evaluation TSH was 496.0 µIU/mL and FT4 0.13 ng/dl). Five weeks after beginning L-T4 treatment TSH normalized (TSH 2.72 µIU/mL , FT4 2.08 ng/dl); nevertheless, only another 5 weeks later we noticed a new worsening of thyroid hormone levels (TSH 31.1 µIU/mL , FT4 1.27 ng/dl), which worsened further (TSH 44.8 µIU/mL, FT4 1.16 ng/dl) even if L-T4 dosage was increased. Anamnesis disclosed that she had been given a carob-bean gum thickened formula to combat gastroesophageal reflux disease (GERD) rather than regular type 1 formula milk. The anti-reflux milk formula was discontinued 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 to be reduced. Carob-bean gum thickened formula may influence the absorption of L-T4. If such formulas are used, we recommend a more frequent evaluation of thyroid function. In CH infants, inexplicably high TSH levels could be caused by gastrointestinal disorders or the interference of drugs or other substances, including some types of milk formula, which impair L-T4 absorption.