Hepatic encephalopathy: etiology, pathogenesis, and clinical signs.

Hepatic encephalopathy (HE) is a manifestation of clinical signs that may result from a variety of liver diseases. In small animals, HE is most commonly a result of portosystemic shunting. The pathogenesis is not completely understood, although it is likely multifactorial. Theories of pathogenesis include altered ammonia metabolism and glutamine and glutamate transmission, an increase in gamma-aminobutyric acid agonists and benzodiazepine-like substances, alterations of the serotonergic system and amino acid metabolism, elevated taurine levels, contributions from inflammatory mediators, and toxic effects of manganese. An understanding of the underlying mechanisms that result in HE may lead to new treatments in the future.