Reye's syndrome is an acute childhood illness that causes fatty infiltration of the liver with increased blood ammonia levels, encephalopathy (degenerative disease of the brain), and increased intracranial pressure. In addition, fatty infiltration of the kidneys, brain, and heart muscle may occur.

Reye's syndrome affects children from infancy to adolescence and occurs equally in boys and girls. It affects whites over age 1 more often than blacks.

The prognosis depends on the severity of central nervous system depression. Previously, the mortality rate was as high as 90%. Today, however, early detection and treatment of increased intracranial pressure, along with other treatment measures, have cut mortality to about 20%. Death is usually a result of brain swelling or respiratory arrest. Comatose children who survive may have residual brain damage.

What causes it?

Reye's syndrome almost always follows within 1 to 3 days of an acute viral infection, such as an upper respiratory infection, type B influenza, or chickenpox. Incidence often rises during flu outbreaks and may be linked to aspirin use.

In this disorder, damaged liver cells disrupt the urea cycle, which normally changes ammonia to urea for its excretion from the body. This results in high blood ammonia and low blood sugar levels and an increase in serum short-chain fatty acids, leading to encephalopathy. Simultaneously, fatty infiltration is found in kidney cells, brain tissue, and muscle tissue, including the heart.

What are its symptoms?

The severity of the child's signs and symptoms varies with the degree of encephalopathy and brain swelling. In any case, Reye's syndrome develops in five stages: After the initial viral infection, a brief recovery period follows when the child doesn't seem seriously ill. A few days later, he or she develops intractable vomiting; lethargy; rapidly changing mental status (mild to severe agitation, confusion, irritability, delirium); rising blood pressure, respiratory rate, and pulse rate; and hyperactive reflexes.

Reye's syndrome often progresses to coma. As the coma deepens, seizures develop, followed by decreased tendon reflexes and, frequently, respiratory failure.

How is it diagnosed?

A history of a recent viral disorder with typical clinical features strongly suggests Reye's syndrome. An increased blood ammonia level, abnormal clotting studies, and evidence of liver dysfunction confirm it. Testing the serum salicylate level rules out aspirin overdose.

Absence of jaundice despite increased liver transaminase levels rules out acute liver failure and other liver diseases.

How is it treated?

Treatment depends on the disease stage. During the early stages, the child typically receives intravenous fluids and a diuretic to decrease intracranial pressure and brain swelling. He or she may also receive vitamin K or fresh frozen plasma. During the middle stage, typified by coma, the doctor may insert a device into the skull to monitor intracranial pressure, and may also start mechanical ventilation and prescribe intravenous Osmitrol. For deepening coma, some pediatric centers use barbiturate coma, decompressive craniotomy, hypothermia, or exchange transfusion.

To prevent Reye's syndrome, parents should give their children nonsalicylate analgesics and antipyretics, such as Tylenol or other drugs containing acetaminophen, instead of aspirin products.