Hepatic Encephalopathy

Hepatic encephalopathy is a syndrome characterized by central nervous system dysfunction in association with liver failure, including portal-systemic shunts (PSS). This condition is usually caused by a birth defect that leads to blood vessel abnormalities within the liver, or in rare cases it may result from an enzyme deficiency in the liver.

Breeds at Risk

Breeds often affected include Miniature Schnauzer, Yorkshire Terrier, Cairn Terrier, Australian Cattle Dog, Old English Sheepdog (Bobtail) and Maltese. This complication of chronic or acute liver disease is a result of the failure of the liver to detoxify toxins originating in the intestine. Because of portal-systemic shunts, these toxic substances bypass the liver, where they normally are metabolized. After bypassing the liver, these toxic substances cross the blood-brain barrier and exert direct or indirect neurotoxic effects on the central nervous system. Toxins from the intestines cross the blood-brain barrier at the level of endothelial cells that line the capillaries in the brain. The blood-brain barrier in patients with hepatic encephalopathy is disturbed, possibly by the toxic effects of ammonia.

Congenital Portal-Systemic Shunts

Congenital PSS is more commonly seen in purebred (Yorkshire terriers and Miniature schnauzers) than in mix-breed dogs. Most animals are presented by 2 years of age, often by 6 months of age, and sporadically at any age. Owners' concerns are commonly related to neurological, gastrointestinal, and/or urinary tract disorders. Furthermore, affected animals may have a history of stunted growth or failure to gain weight compared with unaffected littermates.

Nervous system signs are usually evident in puppies before they are 6 months of age. Signs include "staring into space," inappropriate barking ow whining, aggression, agitation. In advance disease, lethargy and confusion (frequently progressing to coma), abnormal involuntary movements which primarily affect the extremities, trunk, or jaw, involuntary movements of the eye, seizures and muscle spasms can be seen.

Diagnosis of Hepatic Encephalopathy

The most common laboratory test used to diagnose hepatic encephalopathy is the measurement of arterial blood ammonium.

Treatment of Hepatic Encephalopathy

The goal of therapy is to control the pathophysiological mechanisms responsible for inducing the encephalopathy, while the liver attempts to regenerate sufficient tissue to maintain life. This is accomplished by reducing the entry, production and absorption of gastrointestinal "toxins" and by administering systemic drugs which counteract the effects of the absorbed toxins. The mainstays of therapy for encephalopathy involve reduction of protein intake, suppression or elimination of urease containing intestinal bacteria, and catharsis. In addition, steps must be taken to recognize and eliminate any precipitating factors which may have induced the encephalopathy. For animals exhibiting signs of encephalopathy all oral intake of food should cease until CNS signs abate. This is particularly important for protein. Cessation of food intake eliminates dietary sources of ammonia, toxic amines, aromatic amino acids, and sort chain fatty acids which induce encephalopathy. Additional supportive measures may be necessary in the management of animals with .hepatic encephalopathy. Parenteral fluid therapy is often required for several days in patients with hepatic failure.