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CANINE LIVER DISEASE The liver lies at the front of the abdomen and is shielded by the overhanging last few ribs. Its functions are numerous and include manufacture of proteins, bile and cholesterol, metabolism of fats and carbohydrates, storage of substances such as fats and iron, contributing to maintaining a steady glucose concentration, and the breakdown of toxins, drugs, and other metabolites. Closely associated with the liver is the gall bladder. This structure stores bile produced by the liver and then, when required, secretes it into the intestine to aid the digestion of food. Causes of liver failure in the dog are many and varied, invariably they present with either acute liver disease or chronic liver disease. Compared to human medicine relatively little is known about many of the infectious diseases of the canine liver. The two main infectious conditions are Infectious Canine Hepatitis and Leptosporosis. Other infections which can involve the liver include Salmonellosis and toxoplasmosis. Traumatic injury is common, often due to incidents such as road traffic accidents resulting in hepatic rupture. Degenerative changes such as fatty infiltration (possibly arising as a result of diabetes or pancreatic problems) and cirrhosis are common in older animals. Drug reactions can occur but have a fairly low incidence. Heart failure can result in circulatory changes in the liver as blood collects and the vessels become congested. Portosystemic shunts are congenital malfunctions which cause blood to bypass the liver. Cancer of the liver is common in older dogs, these tumours can be primary or secondary, and benign or malignant. It is important to differentiate cancer from nodular hyperplasia which although producing nodules in the liver, normally does not affect liver function. Methods of diagnosis and investigation of liver disease Clinical signs Animals affected often have lethargy, inappetance, diarrhoea, vomiting, weight loss, jaundice, pale gums, abdominal swelling, bleeding disorders, and sometimes nervous signs can also develop. Many of these signs can develop with other conditions as well so confirmation of diagnosis often requires further investigation. Blood testing Liver enzymes such as AST, ALT, ALKP, or GGT can be of use. AST and ALT are released from damaged liver cells, ALKP and GGT are raised in situations that cause a blockage in bile flow. Some of these enzymes can be raised by other conditions or drugs (for example steroid treatment can result in a raised level of ALKP). Bilirubin is a substance which is released from blood cells and then secreted in bile by the liver. In situations of liver cell damage it can show a raised blood level. Albumin is a blood protein produced only in the liver, low levels can indicate liver failure, but can also occur in some intestinal and kidney conditions due to excessive loss of the protein. Ammonia is produced from protein breakdown in the intestine and is then transported to, and metabolised in, the liver. Increased ammonia concentrations will occur in portosystemic shunts or in liver failure. Bile acids are produced by the liver and secreted into the intestine during digestion of food, assessment of the changes in the level of bile acids, especially around the time of feeding, can indicate liver malfunction. The liver is responsible for the production of blood clotting proteins. Liver failure can therefore result in a lower level of these proteins, causing an inability to clot the blood and predisposing to bleeding disorders. Abdominal fluid Animals in liver failure can collect fluid in the abdomen, giving them a pot bellied appearance. Removing some of this fluid by a process called paracentesis and analysing it can give an indication of the type of disorder. X-rays / Ultrasound These are useful to determine the size and texture of the liver, enlargement of the liver can occur with cancer, in portosystemic shunts the liver is usually small. Biopsy Biopsy can be carried out with needles passed through the body wall, or tissue samples can be removed during an exploratory laparatomy, this procedure does carry some risks in those cases with blood clotting problems. Treatment and Management of liver disease Management of liver failure requires special dietary regulation. Protein levels have to be carefully controlled to maintain low blood ammonia levels since rising levels of ammonia result in neurological problems. To achieve this a balanced protein diet must be used, carbohydrates will provide most of the energy requirements and fat levels should not be excessive. The best way to achieve this is to use a commercial prescription diet as recommended by your veterinary surgeon. The limited use of diuretics (spironolactone or frusemide) can be useful in those cases experiencing fluid build up in the abdomen. Antibiotics can be useful to prevent septicaemia developing as the liver may be unable to remove bacteria absorbed from the intestine. In certain breeds drugs to reduce copper levels are appropriate, and if bleeding disorders are developing then Vitamin K supplementation is recommended. In those cases at risk of developing neurological signs lactulose can help to reduce ammonia production in the intestinal tract by altering the normal bacterial function. In cases of acute liver failure it is important to correct the abnormalities created by liver dysfunction, this is often helped by aggressive intravenous fluid therapy. |
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