A 2-day-old boy is evaluated in the newborn nursery for jaundice. He was born to a 24-year-old primigravid woman who is in good health. The mother consumed a well-balanced diet and took prenatal vitamins throughout the pregnancy. The infant is breastfeeding poorly, with a weak latch and suck. On examination, the patient has jaundice, scleral icterus, a large tongue, and a hoarse cry. His tone is normal but his activity is decreased. Laboratory results are as follows:
Total bilirubin 15.3 mg/dL Direct bilirubin 0.7 mg/dL TSH 110 µU/mL Thyroxine (T4), serum 0.6 µg/dL
Which of the following is the most likely cause of this infant's condition?
Congenital hypothyroidism | |
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*Avoid coadministration with soy products, iron, or calcium. | |
Newborn screening programs universally test for congenital hypothyroidism, which is characterized by elevated TSH levels and decreased T4 levels. This infant's jaundice, decreased activity, poor feeding, and hoarse cry are typical symptoms of congenital hypothyroidism. However, most infants with hypothyroidism are asymptomatic and identified through newborn screening. The most common cause of congenital hypothyroidism worldwide is thyroid dysgenesis (eg, aplasia, hypoplasia, ectopic gland). Prompt recognition and thyroid hormone replacement (eg, levothyroxine) is necessary to prevent permanent neurodevelopmental injury.
(Choice A) A variety of defects in the synthesis of thyroid hormone can lead to congenital hypothyroidism, but these conditions are rare relative to thyroid dysgenesis. All known conditions of defective synthesis are inherited in an autosomal recessive pattern.
(Choice B) Maternal iodine deficiency can cause neonatal hypothyroidism; introduction of iodine into the infant diet can reverse this condition. However, iodine deficiency or endemic goiter is uncommon in the developed world, and this mother's nutritional status was good throughout the pregnancy.
(Choice C) Deficiency of TSH due to pituitary failure (panhypopituitarism) is a serious condition, as it is usually associated with ACTH deficiency and impending adrenal shock. However, this infant has elevated levels of TSH, demonstrating that the pituitary is functioning.
(Choice E) Maternal Graves' disease can lead to transplacental passage of TSH-receptor antibodies. Affected infants have signs of hyperthyroidism (thyrotoxicosis) including jitteriness, tachycardia, weight loss, and poor feeding.
Educational objective:
Congenital hypothyroidism is associated with neurodevelopmental injury if not recognized and treated early. Decreased activity, hoarse cry, and jaundice are commonly associated with congenital hypothyroidism, but the majority of infants with congenital hypothyroidism are asymptomatic. Thyroid dysgenesis is the most common cause of congenital hypothyroidism worldwide.