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Retired NBME 25 Answers

nbme25/Block 2/Question#25 (reveal difficulty score)
A 3-year-old boy is brought to the emergency ...
Mitochondria ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—shak360(19)
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I thought this question was difficult because I tunnel-visioned on the diagnosis being hepatic encephalopathy (which it somewhat is), but it is hepatic encephalopathy secondary to Reye syndrome.

Mitochondrial dysfunction is associated with the pathogenesis of Reye syndrome, which is associated with salicylate use (such as aspirin) in children preceding viral infection. Usually, a VZV or influenza infection is treated with aspirin, and aspirin metabolites decrease beta-oxidation by reversibly inhibiting MITOCHONDRIAL enzymes. These mitochondrial abnormalities are associated with SHINE:

  • Steatosis of liver and hepatocytes (impaired beta-oxidation of fatty acids)
  • Hypoglycemia and hepatomegaly
  • Infection (VZV, Influenza)
  • Not awake (coma)
  • Encephalopathy

You want to avoid aspirin in children, except in those with Kawasaki (mucocutaneous lymph node syndrome) disease.

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Hepatic encephalopathy is a disease where cirrhosis and portosystemic shunts can lead to decreased NH3 ammonia metabolism leading to neuropsychiatric dysfunction. It can be triggered by increased ammonia production and absorption due to a GI bleed, constipation, or decreased ammonia excretion. The treatment is lactulose which increases ammonium ion NH4+ generation and rifaximin which decreases the number of ammonia-producing bacteria. Glutamate transporters do not have a known role in the pathophysiology of Reye syndrome, but they are implicated in the pathophysiology of hepatic encephalopathy, which occurs when ammonia joins with glutamate in the brain.

+/- shak360(19)

See this question on lactulose also in the block.

+/- shak360(19)

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