Hyperthyroidism in the newborn is usually caused by Graves disease in the mother.
Symptoms include irritability, rapid heart rate, bulging eyes, and delayed weight gain.
The diagnosis is based on thyroid function tests.
This disorder can be fatal if left untreated.
Treatment typically includes antithyroid drugs and beta-blockers.
The thyroid gland secretes thyroid hormone. Thyroid hormone controls the speed of the body's metabolism, including how fast the heart beats and how the body regulates temperature. If the thyroid gland produces too much thyroid hormone, these functions speed up.
Hyperthyroidism, or Graves disease in the newborn (neonatal Graves disease), is rare in newborns but is potentially fatal if not recognized and treated by a medical doctor who specializes in disorders of the endocrine glands in children (pediatric endocrinologist). This condition usually occurs if the mother has Graves disease during pregnancy or has been treated for it before pregnancy. In Graves disease, the mother’s body produces antibodies that stimulate her thyroid gland to produce increased amounts of thyroid hormone. These antibodies cross the placenta and also cause the fetus's thyroid gland to produce too much thyroid hormone, which can result in death of the fetus or premature birth. Because newborns are no longer exposed to the mother's antibodies after birth, Graves disease in the newborn is usually temporary but may come back.
An affected newborn has increased bodily functions, such as a rapid heart rate and breathing, irritability, and excessive appetite with poor weight gain. Other symptoms include failure to thrive, vomiting, and diarrhea. The newborn, like the mother, may have bulging eyes (exophthalmos). If the newborn has an enlarged thyroid gland (congenital goiter), the gland may press against the windpipe and interfere with breathing at birth. A very rapid heart rate can lead to heart failure. Untreated hyperthyroidism may result in early closing of the bones of the skull (craniosynostosis), intellectual disability, growth failure, short stature, and hyperactivity later in childhood.
The results of the routine screening blood test done in the hospital after birth to evaluate thyroid function, which is done mainly to look for hypothyroidism, may reveal hyperthyroidism.
Doctors suspect hyperthyroidism if the newborn's mother has Graves disease and if the newborn has typical symptoms.
Doctors then confirm the diagnosis by doing blood tests called thyroid function tests to detect elevated levels of thyroid hormone and thyroid-stimulating antibodies from the mother in the newborn’s blood.
After hyperthyroidism of the newborn is diagnosed, doctors may do imaging tests to evaluate the size and location of the thyroid gland.
Infants who have neonatal Graves disease almost always recover within 6 months. If the mother did not take drugs that decrease the thyroid gland's production of thyroid hormones (antithyroid drugs) while pregnant, the infant will have hyperthyroidism at birth. If the mother did take the drugs while pregnant, the infant may not show symptoms of hyperthyroidism for about 3 to 7 days after birth. (See also treatment of Graves disease during pregnancy.)
Newborns with hyperthyroidism are treated with antithyroid drugs that slow the production of thyroid hormone by the thyroid gland (such as methimazole). They also are given beta-blockers, which slow the heart rate (such as propranolol). Infants may also be given drops of iodine by mouth or hydrocortisone by vein if other therapies have not helped. These drugs are stopped as soon as the antibodies that cross the placenta from the mother have disappeared from the infant’s bloodstream.