Reye's syndrome is defined by the Centers for Disease Control and Prevention as an acute, noninflammatory encephalopathy with altered levels of consciousness and liver dysfunction. y The liver disease must include either fatty metamorphosis of the liver or at least a threefold increase in alanine aminotransferase, aspartate aminotransferase, or serum ammonia.
Pathogenesis and Pathophysiology. A growing body of evidence suggests that Reye's syndrome may be a multiorgan disease due to diffuse mitochondrial injury of unknown origin.y , y Mitochondria in hepatocytes, brain capillary endothelial cells, neurons, cardiac and skeletal muscle fibers, and pancreatic cells show histological damage. Liver mitochondrial enzyme activity is low. y In one study, several depressed electron transport enzymes and lowered ATP/adenosine diphosphate (ADP) ratios were documented.y Epidemiological studies strongly associate three virus infections (influenza B, influenza A, and varicella-zoster (see Chapte.r..4.1 ) with Reye's syndrome, although the mechanism of their involvement with the pathogenesis of the condition is unclear. There is no evidence of full viral replication in the two primary organs of damage: liver and brain. It has been suggested that viral proteins are toxic, that the infection causes release of toxins, or that the viral infection plus endogenous or exogenous cofactors, such as salicylates, aflatoxins, insecticides, or certain oils, combine to damage liver and brain.
Epidemiology and Risk Factors. Reye's syndrome occurs worldwide. In the United States, from 1982 to 1985, the incidence was approximately 0.3 in 100,000 persons, and the rate has been relatively stable since then. y There is no solid evidence to establish a genetic basis for Reye's syndrome, and only a few cases occur within families.y There may be two epidemiological patterns: (1) an epidemic form, not noted since the 1980s, that occurred mainly in winter and early spring, clustering in time and geographical region, and associated with outbreaks of influenza B and A, and (2) endemic Reye's syndrome with sporadic occurrence and associated with other viral infections, specifically varicella. Most Reye's syndrome cases associated with varicella occur in children between 5 and 9, whereas influenza type B-associated disease occurred in children aged 10 to 14. Salicylate usage has been associated with Reye's syndrome and the reduction in cases seen in the past years has been specifically linked to reduced salicylate ingestion in children. W]
Clinical Features and Associated Disorders. The clinical manifestations can be divided into a prodromal phase and the syndrome itself. During the prodrome, there is an upper respiratory tract infection in 60 to 80 percent of cases, and most documented cases have demonstrated influenza B, A, or varicella-zoster virus. During stage I of Reye's syndrome, vomiting is the primary feature. It is not known whether this effect is due to brain stem dysfunction or a systemic cause, but it is usually abrupt in onset and unremitting. The child becomes irritable and gradually lethargic. Most patients recover from this stage and never develop severe agitation and coma. With stage 2, restlessness and disorientation predominate, along with signs of dysautonomia, tachycardia, sweating, and dilated pupils. Seizures may develop, but status epilepticus is rare. With stage 3, coma ensues, with papilledema developing over 2 to 3 days but without lateralizing signs of focal neurological damage. Seizures develop in approximately half of these patients. In stage 4, there is cerebrate posturing and respiratory dysfunction. The coma of stage 5 is associated with flaccid tone and no response to painful stimuli. Brain stem reflexes, like cold caloric testing (see Chapter!, ) are minimal or absent.
Evaluation and Differential Diagnosis. Laboratory studies during the prodromal phase are not diagnostic. Once vomiting develops, alanine aminotransferase and aspartate aminotransferase levels are often very high, often 20 to 30 times normal, but ammonia levels are in the normal range. As coma develops, ammonia levels increase threefold or more over the normal range. Other abnormalities of laboratory tests occur with increases in lactic acid and organic acids, suggesting a blend of respiratory alkalosis and metabolic acidosis, sometimes with hypoglycemia, especially in children younger than 3 years of age. Prolonged prothrombin times develop, but hemorrhaging is rare. The EEG is abnormal with diffuse slowing, and sometimes, burst suppression activity (see Chapter..24 ), but there is no specific pattern of diagnostic value. Liver biopsy shows highly characteristic fatty metamorphosis without inflammation. Neuroimaging with CT or MRI shows a normal brain or diffuse cerebral edema with ventricular compression. Diseases that should be excluded in the diagnosis are encephalitis and meningitis, UCDs, BCAA disorders, and other enzyme deficiency states, including propionicacidemia, glutaricaciduria, and disorders of ketogenesis. Finally, inadvertent intoxication with insecticides, salicylates, methyl bromide, margosa oil, and lead can give a combined picture of encephalopathy and hepatic damage in a young child.
Treatment and Prognosis. There is no specific therapy, and management is aimed at monitoring vital functions, correcting liver abnormalities, and controlling increased intracranial pressure until the disease runs its natural course. Hospitalization in an intensive care unit is recommended, because mental status and respiratory function can change abruptly. Salicylates must not be used, and serum glucose levels must be monitored. Vitamin K is often administered, and anticonvulsants are used to treat clinical seizures and sometimes subclinical epileptic activity that is evident on the EEG. Treatment of the hyperammonemia is particularly problematic because dialysis and exchange transfusions do not markedly reduce ammonia levels or improve outcome. Increased intracranial pressure is a major danger, and some centers use monitoring technology
(see C,h.,apter...26 ) to provide a constant assessment of shifts in pressure gradients. The goal is usually to keep intracranial pressure below 20 mm Hg with a mean cerebral perfusion pressure (mean blood pressure minus mean intracranial pressure) maintained at 60 to 90 mm Hg.
Overall, mortality currently is 30 to 35 percent. Predictors of poor outcome appear to be young age, especially infants younger than 2 years old; high clinical stage at the time of hospital admission; rapid progression from vomiting to coma; maximal clinical stage; high creatine kinase levels; and ammonia levels above 300 pg/dl at the time of hospital admission. In those surviving, hepatic recovery is full but nervous system residua are many. Behavioral problems include attention difficulties, retardation, and aggressive impulsivity. Neurological problems include hemiparesis and quadriparesis, dysarthria, cortical blindness, and seizures. Even among children believed to have full recovery, 34 percent had measurable deficits in school achievement, visuomotor integration, sequencing, and problem solving. y
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