Step 1 topics → Gastrointestinal → Reye Syndrome

Reye Syndrome

USMLE Step 1 trap: Expects inflammatory necrosis in Reye syndrome rather than non-inflammatory microvesicular steatosis. Reye syndrome causes microvesicular steatosis from mitochondrial dysfunction without significant hepatic inflammation or necrosis.

Reye syndrome is a rare but high-yield-concept disorder of childhood tested on USMLE Step 1 through biopsy pattern recognition and mechanism, not clinical diagnosis. It is characterized by acute encephalopathy and liver dysfunction following aspirin use during a viral illness — classically influenza B or varicella. The liver pathology is distinctive: microvesicular steatosis from mitochondrial dysfunction, not the inflammatory necrosis you see in hepatitis. Students consistently conflate Reye syndrome with viral hepatitis and expect inflammation and necrosis on biopsy — that's wrong, and the exam will hand you a biopsy description designed to expose exactly that confusion.

Reye syndrome is a mitochondrial dysfunction story: aspirin metabolites impair beta-oxidation of fatty acids, causing fat to accumulate in hepatocytes as small droplets (microvesicular steatosis). There's no significant inflammatory infiltrate. Clinically, kids present with vomiting and altered mental status after what seemed like a recovering viral illness, often after being given aspirin at home.

The epidemiological angle is the other hook: aspirin is contraindicated in children with viral infections specifically because of this syndrome. Know why aspirin is on the 'do not give' list for pediatric fevers, and know what the liver looks like if it does happen.

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Common misconceptions

Common mistake
Wrong: Reye syndrome causes hepatocellular necrosis visible as inflammation on biopsy.
Right: Reye syndrome causes microvesicular steatosis from mitochondrial dysfunction without significant hepatic inflammation or necrosis.
Reye syndrome does not cause the hepatocellular necrosis and inflammatory infiltrate you see in viral hepatitis. The injury is mitochondrial: aspirin metabolites impair fatty acid beta-oxidation, causing lipid to accumulate in hepatocytes as tiny droplets — microvesicular steatosis. On biopsy, you see fat-laden hepatocytes without significant inflammation, which is the opposite of what students expect when they hear 'liver damage from a virus.'
Common mistake
Gap: Misses the specific aspirin-viral illness combination that triggers Reye syndrome
Reye syndrome is triggered by aspirin use during a viral illness (classically influenza B or varicella) in children, which is why aspirin is contraindicated in pediatric viral infections.
Reye syndrome requires a specific combination: aspirin use PLUS an active viral illness (classically influenza B or varicella) in a child. Aspirin alone doesn't cause it, and the viral illness alone doesn't cause it. This is why aspirin is contraindicated in all pediatric viral infections — you can't always confirm which virus it is, and the risk of triggering Reye syndrome is the reason acetaminophen or ibuprofen are used instead for fever management in children.
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What the exam tests

  1. Given a pediatric patient with encephalopathy and liver dysfunction after aspirin use during influenza or varicella, identify the mechanism as mitochondrial dysfunction leading to microvesicular steatosis — not hepatocellular necrosis or inflammation.

Can you avoid these mistakes?

A 7-year-old recovering from influenza was given aspirin for fever. Three days later he develops intractable vomiting and confusion. Liver biopsy is obtained. What histologic finding do you expect, and what cellular organelle is primarily dysfunctional?
A parent asks why their feverish 5-year-old cannot be given aspirin for their confirmed influenza. Explain the mechanism behind the contraindication and name the two viruses classically associated with this risk.
A biopsy shows hepatocytes packed with small lipid droplets and no significant inflammatory infiltrate. What condition does this pattern suggest, and how does it differ from the biopsy findings of acute viral hepatitis?
On rounds, a medical student tells you that a child with known Reye syndrome has 'liver inflammation from aspirin toxicity.' Correct this statement — what two things are wrong with it?

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