Cause: underlying disorders eg congenital portosystemic shunts (PSS) , urea cycle enzyme deficiencies or acquired PSS secondary to other hepatic disease.
Signs: alteration in behavior, eg head pressing, disorientation, seizures, ataxia, depression and collapse +/- gastrointestinal signs, weight loss.
Episodes may be related to feeding.
Hypersalivation is a common manifestation in cats.
Diagnosis: signs and biochemical assays.
Treatment: reduction in ammonia and mercapten production; antibiotics and reduced protein diet.
Emergency if in hepatic coma.
Prognosis: acute crisis can often be managed; long term prognosis depends on cause of liver dysfunction.
Presenting signs
History: abnormal behavior, often episodic in nature.
Clinical signs:
Disorientation.
Head pressing.
Seizures.
Ataxia .
Acute presentation
Hepatic coma.
Age predisposition
Congenital portosystemic shunts: usually < 1 year (may present later).
Urea cycle enzyme deficiencies: young (6 months to 3 years).
Chronic hepatic disease: usually older individuals.
Cost considerations
Surgical ligation of congenital portosystemic shunts .
Medical management of acquired shunts.
Special risks (e.g. anesthetic) General anesthesia
Reduced metabolism and increased activity of anesthetic drugs particularly phenothiazines, barbiturates and benzodiazepines.
Hypoxia due to seizure activity and compromise of the airway will lead to cytotoxic brain edema and possibly raised intracranial pressure, therefore oxygen supply should be monitored carefully.
Monitoring portal venous pressure to avoid portal hypertension due to the ligating process will reduce complications.
Blood is diverted away from the liver thus preventing toxins from being metabolized.
Acquired portosystemic shunts
Secondary to chronic hepatic disease: end-stage hepatic fibrosis leads to increased resistance to intrahepatic blood flow causing collateral circulation pathways to develop which bypass the liver. Acquired shunts are very rare in cats.
Predisposing factors General
Portosystemic shunts .
Chronic hepatic disease
Urea cycle enzyme deficiencies .
Pathophysiology
Portal blood bypassing liver (congenital shunts) and/or hepatic dysfunction toxins accumulating in the blood neurological deficits.
Toxins implicated include:
Ammonia.
Methionine.
Reduced branched chain amino acids.
Increased short chain fatty acids.
Increased aromatic amino acids.
There are several theories as to the pathogenesis of hepatic encephalopathy and origin is probably multifactorial.
Excess [blood ammonia ] produced by action of gut bacteria on dietary protein is probably important.
Hepatic dysfunction changes in the circulating amino acid composition - decrease in the concentration of branch chain amino acids and increase in the concentration of aromatic amino acids.
Branch chain amino acids are required for the production of excitatory neurotransmitters, levels of which decrease.
Aromatic amino acids are metabolized to produce 'false' neurotransmitters, which increase in concentration, thus causing the neurological signs.
Affected individuals may be in poor body condition.
Clinical signs
Hypersialism .
Disorientation.
Head pressing.
Seizures.
Ataxia.
Collapse.
Signs often episodic.
Hepatic coma.
Diagnostic investigation Biochemistry
Raised serum bile acids pre- and post-prandially (in portosystemic shunts). This test has now superceded bromosulfthalein retention test and ammonia tolerance test.
Elevated [fasting ammonia] .
Low blood [urea] .
Raised alkaline phosphotase .
Reduced [albumin] (uncommon in cats).
Ammonium biurate crystalluria.
Hematology
Red cell microcytosis .
Radiography
Small liver outlines on plain radiographs in about 50% of congenital portosystemic shunts.
Contrast radiography
Contrast venography may reveal presence and position of a portosystemic shunt .
2-D Ultrasonography
Identification of shunts .
May reveal radiolucent renal calculi in bladder .
Altered hepatic echogenicity in acquired portosystemic shunts.
Scintigraphy
Administration of per rectum Technetium 99 produces increased fraction in heart before hepatic uptake in animals with portosystemic shunts.
Confirmation of diagnosis Discriminatory Diagnostic features
Fluid therapy in hepatic coma. Avoid fluid overload.
If necessary administer mannitol (0.5 g/kg IV) if cerebral edema suspected.
Starve and give parenteral +/- colonic antibiotics and lactulose enemas to reduce ammonia production and absorption.
Decrease colonic toxin production and absorption by the use of enemas (20% lactulose TID).
Intravenous branch chain amino acids in hepatic coma have been used experimentally.
Standard treatment
Surgical ligation of shunt (congenital portosystemic shunt).
Medical management
Restricted protein diet . Feed maximal protein level without development of neurological signs since over restriction can seriously affect liver's ability to regenerate.
Oral antibiotics eg ampicillin or metronidazole to reduce the population of bacteria in the large intestine.
Lactulose (0.5 ml/kg TID titrating dose to produce soft but not loose motions).
Fluid therapy if in hepatic coma. Ensure animal is not hypoglycemic or hypokalemic and supplement fluids appropriately if these complications develop.
Monitoring
Monitor blood albumin levels if dietary protein restricted.
Acquired shunts are very rare in cats.
toxins accumulating in the blood 
Avoid fluid overload.
