Hyperthyroidism in infancy is a serious, potentially life-threatening illness, whereas hyperthyroidism developing in childhood produces untoward effects primarily on the cardiovascular and nervous systems that disrupt physical and emotional health. The most common cause of hyperthyroidism in infancy is neonatal Graves' disease, a transient condition resulting from transplacental passage of maternal thyrotropin receptor-stimulating antibody. Fetal tachycardia and a goiter seen on ultrasound examination may lead to prenatal detection. After birth, these infants have poor weight gain despite a voracious appetite, irritability, and disturbed sleep. They are usually successfully treated with antithyroid drugs and β-adrenergic blockers. A significant proportion of these infants develop some degree of mental impairment, probably the result of the effects of hyperthyroidism on the developing central nervous system. Persistent cases of neonatal hyperthyroidism are now recognized to be the result of activating mutations in the thyrotropin receptor. Childhood Graves' disease appears to result from a genetic predisposition and environmental trigger, leading to a failure of immune surveillance and production of thyrotropin receptor-stimulating antibody. Nearly all children with childhood Graves' disease have a goiter and two thirds have some form of ophthalmopathy, although the latter is usually mild. Suppression of serum thyrotropin concentration is the diagnostic laboratory hallmark. Most children are successfully treated with antithyroid drugs, with radioiodine therapy being a more accepted second treatment choice. Whereas Graves' disease accounts for over 90% of childhood hyperthyroidism, other causes of hyperthyroxinemia, such as 1) hyperfunctioning adenomas resulting from mutations constitutively activating the thyrotropin receptor or the alpha subunit of the G protein and 2) pituitary resistance to thyroid hormone, are increasingly recognized.
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