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HIGH-YIELD FACTS

  • The most common disorder causing thyrotoxicosis in children is Graves’ disease.

  • Thyroid hormones upregulate β-adrenergic receptors, causing symptoms of sympathetic nervous system overactivity.

  • Signs of sympathetic hyperactivity include tremor, brisk deep tendon reflexes, tachycardia, arrhythmia, flow murmur, and congestive heart failure (CHF).

  • Precipitating factors for thyroid storm in a patient with hyperthyroidism are stress, palpation of a goiter, iodinated contrast dyes, withdrawal of antithyroid medications, radioiodine therapy, and thyroid surgery.

  • Thyroid storm is suggested by severe hyperpyrexia, delirium or psychosis, severe gastrointestinal hyperactivity, hepatic dysfunction with jaundice, arrhythmia, and CHF.

  • Treatment consists of antithyroid treatment with methimazole, adrenergic blockade, and supportive management.

Thyrotoxicosis refers to a hypermetabolic clinical syndrome due to excess production and secretion of endogenous (i.e., hyperthyroidism), or exogenous thyroid hormones. The term thyroid storm refers to an extreme state of decompensated thyrotoxicosis that is a potentially fatal thyroid emergency.

EPIDEMIOLOGY

The most common cause of hyperthyroidism in children is Graves’ disease. This disease occurs in 1 in 5000 children, with a peak incidence between 11 and 15 years of age. The male to female ratio is 1:5.1 Although the true incidence of childhood thyrotoxicosis is unknown, 5% of all thyrotoxicosis occurs in childhood,2 and 0.6% to 10% of neonates born to mothers with Graves’ disease will show signs of thyrotoxicosis.3 The reported mortality in neonatal thyrotoxicosis is as high as 20%.3 Because childhood hyperthyroidism occurs mostly in adolescents, thyroid storm also occurs more frequently in this group (Fig. 79-1).2

FIGURE 79-1

Etiology and pathophysiology of thyrotoxicosis and thyroid storm.

PATHOPHYSIOLOGY

Thyrotoxicosis results from thyroid hormone excess caused by either overproduction of thyroid hormone by the thyroid gland or by administration of synthetic hormone. Increased concentration of serum free thyroid hormone is almost always found in thyrotoxicosis. In Graves’ disease, activated B-lymphocytes produce antibodies against antigen shared by the thyroid gland and eye muscle.1,4 Thyrotropin receptor-stimulating antibodies (TRSAb) bind to TSH receptors to increase thyroid hormone production. In congenital hyperthyroidism, transplacental transfer of TRSAb from the mother with Graves’ disease stimulates the thyroid gland to cause hyperthyroidism or thyrotoxicosis.1,3,5

The actions of thyroid hormone at the cellular level include calorigenesis, acceleration of substrate turnover, amino acid and lipid metabolism, and stimulation of water and ion transport. Thyroid hormones also activate the adrenergic system by upregulation of β-adrenergic receptors causing symptoms of sympathetic nervous system overactivity, including hyperthermia. Why some individuals with hyperthyroidism have few symptoms and others develop the extreme clinical manifestation of thyroid hormone excess (thyroid storm), is still poorly understood. In thyroid storm, the clinical manifestations of thyroid hormone excess are thought to be because of an uncoupling of oxidative phosphorylation secondary to the illness, resulting in ...

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