The liver is the largest internal organ of the body and it is responsible for a number of metabolic, functional and detoxification processes. It is located in the abdomen, under the diaphragm. The liver is the only organ in the body that is capable of rejuvenating itself.
Functions of the liver include:
Cleans the blood, removing medications and toxins.
Regulating chemicals in the blood.
- Produces and secretes bile, which aids digestion and absorption of fats. Bile is a greenish-yellow fluid which consists of bile acids and waste products such as bilirubin. It is made by the liver and stored in the gall bladder.
- Breaks down haemoglobin creating metabolites that are added to bile as pigment (bilirubin).
- Produces specific enzymes which aid digestion of food.
- Converts most sugars into glycerine which it stores up as glycogen until required.
- Fat-soluble vitamins A, D, E and K need bile in order to be absorbed by the body, these vitamins are stored in the liver.
- Production of blood clotting factors.
- Manufacture of certain hormones.
- The liver changes ammonia, a toxic by-product of protein metabolism into urea, which is excreted in the urine.
The liver is divided into sections (known as lobes), each of which is composed of thousands of structural and functional units (hepatic lobules).
Two blood vessels enter the liver. The hepatic portal vein contains de-oxygenated blood from the spleen, pancreas, and digestive system and the hepatic artery contains oxygen-rich blood from the lungs.
Liver disease occurs when the liver is damaged, resulting in loss of function. It can be acute (sudden onset) or chronic (slow and progressive). There are several causes of liver disease in cats, which include:
- Hepatic Lipidosis (also known as Idiopathic Hepatic Lipidosis or Fatty Liver Disease). Hepatic Lipidosis is the most common type of liver disease in the cat and occurs when your cat becomes anorexic (stops or reduces the amount of food he is eating), the body begins to use fat stores as fuel. These fat stores are sent to the liver, to be broken down to supply nutrients. Unfortunately, the liver sometimes becomes overwhelmed and is unable to process this fat as quickly as necessary, leading to a build up of fat in the liver, which interferes with normal liver function.
- Cholangitis/cholangiohepatitis complex: This is a number of related inflammatory and or infectious disorders of the liver and/or the biliary tract. Cholangitis relates to infection or inflammation of the bile duct and cholangiohepatitis is inflammation of the biliary system and by extension the liver. Causes of infection may often include FIP, Pancreatitis, inflammatory bowel disease (IBD), bacterial infection, parasitic infection (including toxoplasmosis).
- Damage by toxins (Toxic Hepatopathy): This is caused by exposure to drugs, toxins or lack of blood to the liver.
- Toxoplasmosis: Caused by an intracellular protozoa known as toxoplasma gondii, most infected cats will show no symptoms of infection, however in some cases damage to various organs can occur, including the liver.
- Cancer: There are many different types of tumour which affect the liver. Primary liver cancer (beginning in the liver) is uncommon in cats. Most cancers of the liver originate from some other site and spread to the liver.
- Portosystemic shunt (also known as liver shunt): Portosystemic shunts are abnormal communications between the portal and systemic venous system which allows intestinal blood to be delivered to the systemic circulation prior to hepatic detoxification. A shunt means that blood bypasses the liver, resulting in blood not being detoxified by the liver and a rise in toxins. Portosystemic shunts may be congenital or acquired, most shunts in cats are congenital (known as CPSS) and cats demonstrate clinical signs within 12 months of age.
Liver disease can occur in cats of any age although in younger cats it's most commonly caused by a portosystemic shunt or toxic hepatopathy (ingestion of toxins or drugs).
What are the signs of liver disease in cats?
Symptoms may vary depending on what has caused liver disease, and symptoms can often be vague and non-specific. Early symptoms you may notice include:
- Loss of appetite (anorexia) - One of the early signs of liver disease in cats.
- Weight loss - Another early sign of liver disease.
As the liver becomes more damaged, further symptoms develop, such as:
- Jaundice (icterus): Signs of jaundice are yellowing of the eyes, skin and mucous membranes. This is caused by hyperbilirubinemia, high levels of bilirubin in the blood. Bilirubin is a yellow bile pigment that is produced by the breakdown of red blood cells.
- Ascites (abdominal effusion) - Build up of fluid in the peritoneal cavity caused by portal hypertension (high blood pressure) in the portal vein of the liver.
- Polyuria (increased urination)/polydipsia (increased thirst).
- Hepatomegaly (enlargement of the liver) or microhepatica (small liver).
- Dark coloured but clear urine caused by the presence of bilirubin.
- Bad breath.
- Seizures - A build up of toxins due to the liver no longer functioning properly can lead to seizures.
How is liver disease diagnosed?
Your veterinarian will perform a physical examination of your cat and will want to run several tests, including a biochemical profile to look at:
- Changes to the liver enzymes ALT (alanine aminotransferase) and AST (aspartate aminotransferase). The ALT test determines the level of this enzyme in the blood, which increases when damage to the liver cells has occurred. AST is an enzyme also found in skeletal and cardiac muscle cells, the brain and red blood cells. Elevated AST in the blood is also an indicator of liver disease, although as it is found in other organs, it is not as specific for liver cell injury as elevations in ALT.
- Bilirubin: This is a major breakdown product of red blood cells. When red blood cells wear out they are trapped in the spleen and destroyed, releasing bilirubin into the blood. This type of bilirubin is called unconjugated. This bilirubin is transported in the blood to the liver, where it is taken up and conjugated (joined with glycuronic acid). This conjugated form may either be stored in the liver cells or excreted into the bile. Bilirubin levels are increased in cats with liver disease, gallbladder disease or have excessive destruction of red blood cells (known as hemolysis).
- Low blood urea nitrogen (BUN), albumin, glucose, cholesterol which reflect the liver's inability to metabolise urea and glucose or produce albumin or cholesterol.
Other tests he may perform include:
- Complete blood count: May reveal the presence of poikilocytes, which are abnormally shaped red blood cells. Anemia may also be present. Reduced white blood cells or platelets may indicate portal hypertension.
- Urinalysis may reveal ammonium biurite crystals and/or bilirubin in the urine.
- Thyroid testing.
- Bile acids tolerance test. This involves taking a blood sample from your cat and then feeding him a fatty meal. Two hours later, a second blood sample is taken. When a cat eats, bile is released into the small intestine to assist with the digestion of fats (lipids). The bile is then absorbed by the intestine and returned back to the liver where it is removed from the bloodstream. In a cat with liver disease, this process doesn't occur as efficiently and levels of bile remain high in the blood.
- Ultrasound: An ultrasound can give your veterinarian an idea of the size and shape of your cat's liver and gallbladder, and detect gallstones and biliary obstruction (blockage of the flow of bile from the liver). Abnormal vessels may be seen on ultrasound. Intrahepatic (inside the liver) are more easy to see on ultrasound than extrahepatic (outside the liver) vessels.
- X-Ray: An x-ray may be taken to give your veterinarian an idea of the size and shape of your cat's liver. X-ray may also detect the presence of tumours.
- Biopsy: A liver biopsy is taken to determine the exact type of liver disease. This may be done at the same time as the ultrasound.
- Serologic Testing: Testing for diseases such as FeLV, FIV, FIP and toxoplasmosis may be taken as these diseases are associated with some liver disorders in cats.
How is liver disease treated?
Treatment depends on the cause of liver disease.
- Intensive nutritional support. Most frequently this involves feeding a calorie dense, high protein food via a feeding tube either directly into the stomach or esophagus. This type of feeding will usually be required for 6 - 8 weeks.
- Fluid and electrolyte therapy if the cat is dehydrated.
- Supportive care with IV or subcutaneous fluids and nutritional support.
- If the cause is bacterial, antibiotics will be prescribed.
- Medication to control vomiting if necessary.
- Corticosteroids may also be helpful in cats.
Damage by toxins:
Immediately stopping the toxins (such as medications) where possible.
Removal of toxins from the body with activated charcoal.