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- What are the investigations required to establish an etiological diagnosis in a
newborn with confi rmed congenital hypothyroidism?
Once a biochemical diagnosis of congenital hypothyroidism is established, new-
borns should be evaluated for the etiological diagnosis. In newborns with pri-
mary hypothyroidism, these include ultrasonography of neck, radionuclide
thyroid scan ( 99m Tc pertechnetate/^123 I scan), serum thyroglobulin, TRAbs, and
urinary iodine levels. In newborns with secondary hypothyroidism, MRI sella,
other pituitary hormones, and ophthalmological evaluation for optic nerve hypo-
plasia should be performed. However, initiation of L-thyroxine should not be
delayed in neonates with congenital hypothyroidism awaiting these investiga-
tions (Fig. 3.6 ). - What are the causes of negative^ 99m^ Tc pertechnetate scan in a neonate with
congenital hypothyroidism?
Absence of tracer uptake in a neonate with congenital hypothyroidism usually
suggests a diagnosis of thyroid agenesis. However, thyroid uptake may be absent
even in the presence of eutopic thyroid gland in conditions like antenatal maternal
iodine exposure, transplacental transfer of TSH receptor-blocking antibodies,
TSH suppression from L-thyroxine treatment, TSH receptor- inactivating muta-
tions, and dyshormonogenesis due to sodium–iodide symporter (NIS) defect.
Therefore, ultrasonography of the thyroid and estimation of thyroglobulin should
be performed to establish the diagnosis of thyroid aplasia (Fig. 3.7 ).
Fig. 3.6 99m Tc
pertechnetate scan in a
child with congenital
hypothyroidism showing
tracer uptake in the lingual
region ( red arrow )
suggestive of ectopic
thyroid
3 Thyroid Disorders in Children