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There are five conditions that affect cat livers which could be called reasonably common. The first is toxic injury -- which may be due to a poisonous substance, to injury from bacterial toxins or from lack of blood supply to the the liver. The second is hepatic lipidosis. This is a metabolic condition that occurs when cats do not eat. There are two problems when this condition occurs, the one that caused the cat not to eat in the first place and the liver failure that results from it. It helps if both conditions can be identified and treated but that is not always possible to do. This condition can appear to come on rather suddenly, much like toxic injury. The third condition that affects cat livers is
cholangiohepatitis, which can show up in several different variations and is a chronic condition. The fourth condition is a group of conditions in which the liver circulation is not functioning correctly, known as portosystemic shunts. The last condition is cancer of the liver. There are several cancers which affect cats which have a tendency to spread to the liver. Figuring out which of these conditions is present involves understanding each of them a little more and also understanding the limitations of lab values and diagnostic techniques which can be used to determine what is happening to the liver.
Lab tests that are commonly used to evaluate liver condition include the ALT (alanine aminotransferase), AST (aspartate aminotransferase) and ALKP (ALP, SAP, serum alkaline phosphatase). These tests do not indicate how the liver is functioning at the present time. They are associated with specific types of damage to the liver and help to determine if these types of damage are a current problem. Liver function can be evaluated using bile acid response testing, which does give an indication of the liver's ability to do its job at the time the test is done. X-rays and ultrasound can give indications of the liver's size and ultrasound can sometimes pinpoint specific lesions in the liver or the gall bladder. Liver biopsy is currently the only sure way to identify many of the liver conditions that affect cats. Liver biopsy can sometimes be done simply by inserting a hypodermic needle into the liver and aspirating contents, a relatively safe procedure or it may involve specialized biopsy needles or exploratory surgery to remove a small wedge of tissue from the liver. Each method of biopsy has its advantages in specific circumstances.
The ALT value is specific to the liver, almost, in cats. A rise in the ALT occurs when the hepatocytes (liver cells) are damaged enough to leak through the cell membrane and release this enzyme. This can occur due to toxins, bacterial infection, blood supply deficiencies, bile duct obstruction and hepatic lipidosis. When an acute injury to the liver occurs the ALT rises rapidly as it is released from damaged cells. In general the level will rise for the first few days and then decrease gradually over two to three weeks if no further injury occurs. This makes the ALT useful in
determining if a liver condition is due to an acute injury or due to ongoing damage, making it a chronic condition. There are times when other systemic illnesses, such as hyperthyroidism or feline leukemia virus infection, can cause enough liver damage to slightly elevate the ALT chronically.
Aspartate aminotransferase (AST) is found in the liver and other organs, including the muscle and brain tissue. Rises in the AST can indicate a problem in any of the organs it is common in, so it is not as specific to the liver. However, when it rises in conjunction with the ALT it can help to confirm that liver disease is present. It may rise faster and to higher levels than the ALT when obstruction to bile flow is present, which can also help to differentiate one cause of liver disease. In order for aspartate aminotransferase to be released, the liver cell usually has to die. Due to this, there can be situations in which the ALT rises because cells are damaged, but the AST remains low because they are still alive. A rise in ALT without any rise in AST would normally be a good prognostic sign since it would indicate damage without cell death.
Alkaline phosphatase (ALP) is found in many tissues but in cats the majority of this enzyme in the bloodstream comes from the liver. This enzyme is excreted in response to bile duct obstruction, making it pretty specific for this problem in cats. It can take awhile for production of the enzyme to start and it will be produced as long as the condition persists, so levels tend to start out low and then rise over the course of an illness in which bile flow is obstructed. Large rises in the ALP level tend to indicate pretty severe obstruction to bile flow which has been present for some time.
These tests show the amount of damage to the liver cells which are present. The reason that they can not be considered "liver function tests" is that a liver with only a few normal cells, such as one in which cancer is
widespread or cirrhosis has occurred, may have little or no cell damage in the remaining cells --- but almost no ability to function. Conversely, a large number of liver cells can suddenly die due to a blood clot or toxin and the rest of the liver can function normally. A large rise in ALT, AST or ALP may occur even though the liver is able to do its job. The test that is currently used to assess the functional ability of the liver is the bile acid response test. Bile acids are removed from the circulation by the liver. If this does not occur, it is a good indication that the liver is not able to function. Bile acid response testing can help to determine if disorders have damaged the liver's ability to do its job and are useful in finding conditions, such as portosystemic blood shunts, in which the functional amount of liver tissue is decreased.
In our practice, hepatic lipidosis seems to be the the most common liver disorder that we encounter. Typically, cats with this condition are refusing to eat. Many of them approach food as if they want it but then refuse to eat at the last minute. If they do eat they may vomit immediately. Some cats do eat and manage not to vomit but only eat small amounts each day, not enough to meet their caloric needs. Cats with this condition appear to be depressed. Often, they are heavy cats prior to the onset of the illness but lose weight rapidly once it starts. As time goes on cats with this condition may develop severe neurologic signs such as head pressing, seizures or coma. Jaundice develops pretty quickly in cats affected by hepatic lipidosis. The best treatment for this condition is aggressive force feeding, often requiring placement of a stomach tube to allow for adequate caloric intake. Hepatic lipidosis is usually fatal if untreated but approximately 80% of cats will recover with aggressive nutritional support. Cats with this condition respond better to high protein, high carbohydrate diets (like kitten foods), which is the opposite of diets prescribed for most other liver conditions. Hepatic lipidosis can often be diagnosed using a fine needle aspirate of the liver, a relatively safe form of biopsy that most veterinary practices are capable of.
We see a fair number of cats that appear to have had toxic insults to their liver for reasons we rarely discover. They are often depressed, often vomiting, sometimes have jaundice and sometimes don't. They also are reluctant to eat. We tend to suspect this problem when the fine needle aspirate doesn't look like hepatic lipidosis but we suspect liver disease based on the lab values and clinical appearance. We look for an underlying cause we can identify and then usually try antibiotic therapy and nutritional support for a few days prior to looking for definite cause because cats with toxic insults often improve fairly rapidly. If the cat is seems to be getting worse we may progress to further diagnostic testing more quickly. It takes a week or two for rises in liver enzyme levels to start to drop towards normal levels in these cats but their attitude and clinical condition seems to improve more rapidly than the lab values.
We also see a fair number of cats with cholangiohepatitis of some sort. There are several types of these disorders. Cholangitis is inflammation or infection of the bile ducts. This is sometimes the first stage of cholangiohepatitis, which is inflammation of the bile ducts and liver tissue. Suppurative cholangiohepatitis is inflammation with pus production. It can be acute or chronic. Cats with this condition tend to have unexplained weight loss, sometimes fevers, decreased appetite, sometimes vomiting and sometimes just a "not doing right" appearance. Antibiotics and medications to stimulate bile flow may be helpful. Surgery can sometimes aid in the treatment of this disease, if a way can be increase bile flow.
Another form of this condition is nonsuppurative cholangiohepatitis. This may be the chronic form of the suppurative condition or it may occur without evidence that suppuration ever occurred. Cats with this condition
often are losing weight but have normal attitudes. They may have occasional vomiting or may not. Often, the first sign that owners notice is yellow discoloration of the white portion of the eyes or the oral tissue. This condition tends to occur in middle aged or older cats but can occur at any age. There are cats with this condition whose liver enzyme levels stay almost normal or only show slight increases. Anemia is often present and as the disease progresses protein levels may decrease in the serum. Even though there is a decrease in protein production by the liver this condition seems to respond better to a low protein (but high quality protein sources) diet than to higher protein. Chronically administered medications are used more commonly in treatment of this condition than in the other liver diseases. Corticosteroids may be helpful. In the end, cirrhosis may occur with either suppurative or nonsuppurative cholangiohepatitis. Diagnosis of the type of cholangiohepatitis and even whether cholangiohepatitis is present often requires biopsy of the liver.
Suppurative cholangiohepatitis may be apparent on surgical exploration of the liver area but it usually is a diagnosis made after examination of a biopsy sample. For this condition biopsy normally requires at least the use of specialized biopsy needles and may require surgical removal of a small section of the liver.
Portosystemic shunts are connections between the arterial and venous blood flow in areas in which that shouldn't occur. This condition is usually congenital and occurs when fetal circulation does not change after birth properly, leading to portions of the liver not receiving adequate blood supply and therefore not functioning properly. Since this occurs at birth most cats with this condition are diagnosed when they are young but cats may not show sufficient clinical signs to make a diagnosis until they are young adults. It has to be considered in cats less than 4 or 5 years old which have unexplained liver disease. Lab values for ALT, AST and ALP are often close to normal or slightly elevated but bile acid response testing shows a severe deficiency in liver function in most cases. Poor growth and neurologic problems such as incoordination, head pressing, blindness and seizures usually are the reasons this condition is brought to the veterinarian's attention.
Liver cancer is not especially common in cats and is usually the result of metastasis of lymphoma or pancreatic tumors to the liver. Some tumors do grow directly from liver tissue. Tumors may show up on X-rays and
ultrasound exams or may be discovered during surgical exploration of the abdomen during a biopsy procedure.
Liver disease of any origin can lead to blood clotting problems because the liver makes most of the clotting elements. Even though this is always theoretically possible with liver disease actual problems from uncontrolled
bleeding after biopsy are not very common. It is still a good idea to test blood clotting prior to doing any type of biopsy other than a fine needle aspirate, though.
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