Changes

==Description==

==Description==

Hepatic encephalopathy is charaterised by a complex of neurological abnormalities that may occur in the presence of advanced liver disease.  By far the most common cause in dog and cat is [[Portosystemic Shunt]].

Hepatic encephalopathy is charaterised by a complex of neurological abnormalities that may occur in the presence of advanced liver disease.  By far the most common cause in dog and cat is [[Portosystemic Shunt]] (PSS) although a marked reduction in functional mass of hepatic tissue can also leads to hepatic encephalopathy.  In rare cases, if severe acquired shunt due to hepatobiliary disease and congenital PSS have been been ruled out, congenital urea enzyme cycle deficiencies and organic acidaemias, where there is lack of ability to degrade ammonia to urea, can be considered.

 

This is a reversible abnormality of the cerebral metabolism.  Its pathogensis is not yet fully understood.  Increased concentration of ammonia level is most common cause of this disease manifestations due to the toxic effect it has on  brain cells.  Due to the lack of urea cycle in the brain, ammonia in cerebrospinal fluid (CSF) is detoxified into glutamine.  Level of glutamine can be shown to correlate with clinical signs.  Aromatic amino acids, especially tryptophan and its metabolites, share an antiport transporter with ammonia in CSF.  Consequently, dogs with congenital PSS are reported to have an increased aromatic amino acid concentrations in CSF.  Increased ammonia concentrations also have a number of other effects on the central nervous system, including a reduction in serotonin activity, an increased in NMDA (N-methyl-D-aspartic acid) and peripheral-type benzodiazepine receptors.