The Centers for Disease Control and Prevention uses a case definition for evaluating patients with possible Reye's Syndrome.
Criteria for Reye's Syndrome
(1) acute noninflammatory encephalopathy
(1a) alteration in consciousness, AND
(1b) either CSF showing <= 8 leukocytes per µL, OR histology showing cerebral edema without perivascular or meningeal inflammation
(2a) histology (biopsy, or at autopsy) considered diagnostic, OR
(2b) increase in either AST (SGOT), ALT (SGPT) or serum ammonia >= 3 times
(3) no more reasonable explanation for the cerebral or hepatic abnormalities
Alteration in consciousness: lethargy to coma
The CSF leukocyte count "<= 8" is from the MMWR; other references use "< 8".
(1) light microscopy: panacinar microvesicular hepatic steatosis with little or no inflammatory cell infiltration
(2) electron microscopy: swelling of mitochondria, with loss of matrical density and with fragmentation and reduction in the number of cristae
Increase in serum markers:
(2a) unclear if rise is based on upper limit of normal or previous values if available
Other explanation for abnormalities:
(1) inborn errors of metabolism: disorders of ureagenesis, ketogenesis and branched-chain amino acids
(2) toxin exposure
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Specialty: Gastroenterology, Pedatrics, Pharmacology, clinical