A 6-hour-old boy is in the newborn nursery with tachycardia. He was born at 40 weeks gestation to a 30-year-old woman with Graves' disease that was treated with surgical resection approximately 6 months before the pregnancy. Subsequently, the mother became mildly hypothyroid and was treated with levothyroxine during the pregnancy. The infant's weight is 2080 g (4 lb 9 oz) (

Question

A 6-hour-old boy is in the newborn nursery with tachycardia.  He was born at 40 weeks gestation to a 30-year-old woman with Graves' disease that was treated with surgical resection approximately 6 months before the pregnancy.  Subsequently, the mother became mildly hypothyroid and was treated with levothyroxine during the pregnancy.  The infant's weight is 2080 g (4 lb 9 oz) (<5th percentile), temperature is 37.2 C (99 F), and pulse is 190/min.  Examination shows an irritable but consolable infant with warm, flushed skin.  Which of the following is the most likely cause of this infant's condition?

Quizplus · Accepted Answer

11ec25c8_d660_ae8b_bc81_3360b7f80665_MD0003_00 This neonate's presentation (maternal history of Graves' disease, low birth weight, tachycardia, warm skin, irritability) is characteristic of neonatal thyrotoxicosis (neonatal Graves' disease). Thyrotoxicosis results from transplacental passage of anti-TSH receptor antibodies during the third trimester. Elevated anti-TSH receptor antibody levels can occur despite maternal treatment for Graves' disease and euthyroidism or hypothyroidism during pregnancy. Neonates born to women with anti-TSH receptor antibodies >5 times the upper limit of normal are at greatest risk. Most infants with thyrotoxicosis are born to mothers known to have Graves' disease. The most severe cases of thyrotoxicosis result in symptomatic fetuses (fetal tachycardia, hydrops, growth restriction.) Symptomatic patients require short-term treatment with methimazole plus a β blocker as neonatal hyperthyroidism has adverse effects on the developing nervous system (eg, growth retardation, developmental/behavioral problems). The condition generally self-resolves over the first few weeks to months of life as maternal antibody disappears from the infant's circulation. (Choice A) Patients with ectopic thyroid tissue (ie, thyroglossal duct cysts) are usually euthyroid or hypothyroid, in contrast to this patient who is hyperthyroid. (Choice B) This infant's mother has been mildly hypothyroid since her thyroidectomy. Excess hormone due to residual tissue is unlikely. In addition, maternal thyroid hormone does not cross the placenta in significant amounts. (Choice C) TSH levels surge in healthy newborns immediately after delivery, leading to a rise in free T4 and T3. This increase in TSH and T4 is physiologic and the basis for neonatal screening for hypothyroidism. Infants with thyrotoxicosis can have suppression of the normal TSH surge. (Choice D) Similar to endogenous thyroid hormone, levothyroxine does not cross the placenta to a significant degree. The fetus makes its own endogenous thyroid hormones. Educational objective: Infants born to women with Graves' disease are at risk for thyrotoxicosis due to passage of maternal TSH receptor antibodies across the placenta. Affected infants are irritable, tachycardic, and gain weight poorly. Methimazole plus a β blocker are given to symptomatic patients until the condition self-resolves over a few weeks to months. References: Fetal and neonatal thyrotoxicosis. (http://www.ncbi.nlm.nih.gov/pubmed/24251220) Hyperthyroidism in pregnancy. (http://www.ncbi.nlm.nih.gov/pubmed/24622372)

A 6-Hour-Old Boy Is in the Newborn Nursery with Tachycardia