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Neonate with Possible Hypothyroidism

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Question

2 month old baby,male, was born full term, birth weight 3.2kg. No neonatal complications. No hipoglicemia, jaundice or micropenis. Normal newborn screening (Normal TSH and Free T4).

Maternal data: no medications during pregnancy or breastfeeding, no problems during pregnancy. Normal Thyroid function test.No hoarse cry, facial puffiness, umbilical hernia, hypotonia, mottling, cold hands and feet or lethargy. Active baby. No dysmorphisms.

During pediatric evaluation: protrusion of tongue and hepatomegaly (3cm) was noted so TFT was ordered at 2 months. Results Free T4 0.94 (normal value1.0 – 2.0); TSH 1.0; normal T3repeated twice in a good laboratory.rT3 and TBG ordered + new TFT in another lab (on the way).

HD: Euthyroid sickness? due to ???? (no aparent cause), 2o or 3o hypothyroidism?,TBG deficiency?

Should we treat if new FT4 is low?Is it crucialto check GH, LH, FSH, PRL, cortisolin the abscence of micropenis and hypoglycemia? Should we perform an MRI? Does protrusion of tongue occur in 2o or 3o hypothyroidism as well? Thanks in advance for your help.

Clarissa Pedreira

Response

I would be concerned about either TBG deficiency or hypopituitarism in the baby. It is unusual to see secondary (or tertiary) hypothyroidism in the absence of growth hormone deficiency as you are aware. I don’t think it is likely to be sick euthyroid syndrome if the baby is not sick.

In addition to checking TBG (as you have done), I would check an IGF-1, IGF-BP3, am cortisoland blood sugars PRIOR to feedings, particularly if the baby is sleeping through the night.There is a mini-“puberty” in the neonatalperiod so you have a unique opportunity to check testosterone, LH and FSH as well. I would also do an MRI to look not only at the pituitary/hypothalamic anatomy but the size of the optic nerves and any midline brain defects, such as absent septum pellucidum or corpus callosum. I would be most interested in follow up of this most perplexing case.

Rosalind Brown MD