Hepatic encephalopathy is associated with elevated blood levels of which toxin that causes neuropsychiatric abnormalities?

• A. Bilirubin
• B. Ammonia
• C. Methanol
• D. Nitric oxide

Answer: (B)

Hepatic encephalopathy is driven by a toxin that the diseased liver can’t clear: ammonia. When liver function is impaired or portosystemic shunting occurs, ammonia produced by gut bacteria from protein isn’t efficiently converted to urea. Ammonia then enters the bloodstream and crosses into the brain, where it is taken up by astrocytes and converted to glutamine. This accumulation causes astrocyte swelling and disrupts neurotransmission, leading to the range of neuropsychiatric abnormalities from subtle cognitive changes to confusion, asterixis, and coma.

Bilirubin reflects cholestasis and liver excretory failure but isn’t the primary driver of the neuropsychiatric symptoms. Methanol is a separate toxin (causing coma with metabolic acidosis and optic injury), and nitric oxide, while involved in various vascular processes, is not the toxin responsible for hepatic encephalopathy.