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Liver Disease in Pets

overview

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What is liver disease?

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Liver disease is a broad term and can refer to a wide variety of problems. The liver is a large organ with significant regenerative capacity (it can replace damaged tissue). This means that many liver conditions have the potential to completely resolve. It also means that liver disease must be widespread before it causes a significant loss of liver function. Inflammation of the liver is known as hepatitis, but this is not specific for any one cause.

Attached to the liver is the gallbladder, a small sac which stores bile ready for digestion. The gallbladder can become inflamed in its own right, known as cholangitis, or can be a component of liver disease. Inflammation of the liver and gallbladder is known as cholangiohepatitis.

Common causes of liver disease in cats and dogs include infections (bacterial/viral), toxic insult, inflammation, immune-mediated, cancer, age-related changes, and changes secondary to other conditions (e.g. Cushing’s disease). Conditions primarily affecting the gallbladder can also lead to changes in the liver.

symptoms

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What are the symptoms of liver disease?

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Liver disease can cause a variety of symptoms including inappetence, vomiting or diarrhoea, lethargy, abdominal discomfort and weight loss. If the flow of bile into or out of the gallbladder is disrupted, pets may become jaundiced (seen as a yellow colour to the oral membranes, eyes and skin).

Many pets with liver disease do not show symptoms, so often the first indication is an elevation of liver enzymes, known as ALT and ALP, on a blood test. ALT is released when liver cells are damaged, while ALP increases if bile flow through the liver is slower than normal.  Elevation in these enzymes suggests something may be affecting the liver but doesn't tell us whether these changes are significant or not. It is very common to find elevated liver enzymes on routine blood tests, such as pre-anaesthetic screens or when monitoring drug use. We can't assume there is serious liver disease from these enzyme levels alone, so further investigations must be performed.

diagnosis

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What tests are used to diagnose liver disease in pets?

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If elevated liver enzymes have not already been identified on a blood test, running bloods will be the first step in pets presenting unwell with symptoms that could be due to liver disease. As described above, we need further testing to know whether an elevation in enzymes is clinically significant.

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Bile Acid Stimulation Test

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Known as a BAST, this is a specific blood test involving two samples taken two hours apart, with a meal in between. The test looks at how the liver responds to the meal and is a good indicator of how the liver is functioning. Liver function is important for metabolism of drugs, including those used during anaesthesia. If the liver is not functioning normally, the BAST result will be increased. There are many possible causes of liver dysfunction, so an abnormal BAST result alone does not give us a diagnosis.

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Ultrasound

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An ultrasound scan lets us assess the structure of the liver. Significant structural changes are easily seen, such as masses on or within the liver. Diffuse disease can show as abnormalities in the texture of the liver but does not always cause visible changes. Depending on what type of disease is suspected, a sample of liver cells may be taken with a needle during the ultrasound (known as a fine needle aspirate). Ultrasound also allows us to examine the gall bladder and other abdominal organs. Most animals will allow ultrasound to be performed either awake or under light sedation. It requires the fur to be clipped over the abdomen but is not a painful procedure.

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Liver function and structural changes do not always correlate - either can cause an increase in ALP and ALT so often both a BAST and ultrasound examination are advised.

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Further blood tests

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Several systemic conditions can cause a secondary increase in liver enzymes, especially endocrine diseases such as Cushing's disease or diabetes. Additional blood tests may be required to rule these conditions in or out.

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Urinalysis

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Liver disease can impair the kidneys ability to concentrate urine, however this is only seen in very progressed disease. If the urine is very dilute this may suggest another underlying condition and can help direct investigations.

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Biopsy

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Ultimately, the only way to know exactly what is happening in the liver is with a tissue biopsy. Sometimes this can be obtained via ultrasound, but more commonly a surgical biopsy is needed. Surgery allows the liver to be examined visually and biopsies can be taken from specific areas. Although this isn't a high-risk surgery, it is advisable to measure the blood's ability to clot beforehand, as the liver has an important role in creating clotting factors. In some clinics, liver biopsies can be performed laparoscopically (keyhole) which is less invasive and may be preferable for unwell animals.

treatment

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How is liver disease treated?

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Treatment of liver disease is non-specific. Commonly, a liver supplementation containing SAMe and silybin will be prescribed to support the liver’s function. If there is evidence that bile flow through the liver is abnormal, a medication called ursodeoxycholic acid may be prescribed. If the pet is unwell, hospitalisation for fluid therapy, anti-sickness medication and/or pain relief may be recommended.

Further treatment will depend on the underlying cause, and could include antibiotics, steroids, chemotherapy, or management of any underlying conditions (such as Cushing’s disease). If a tumour affecting the liver is found, it may be possible to manage this surgically depending on the size and which part of the liver is affected.

Not all pets with increased ALP or ALT have significant liver disease. Some changes are transient, and caused by an acute insult such as trauma, ingestion of something mildly toxic, or a reaction to medication. If your vet suspects there is not significant liver disease present, they may suggest repeating the blood test in 3-6 weeks to see if the enzymes have lowered, with or without a course of medication to support the liver.

outlook

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What is the outlook for pets with liver disease?

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The prognosis for pets with liver disease varies depending on the underlying cause. Many conditions affecting the liver are treatable, especially given the liver’s ability to regenerate, so there is often a good chance for complete recovery. Some conditions are permanent but manageable; in these cases, pets may need long-term treatment to support the liver but still have a good prognosis. Less commonly, liver disease is due to incurable conditions such as cancer. Tumours that can be surgically removed carry a good prognosis, while other cancers may shorten a pet's lifespan. The same is true for liver failure, in which there is not enough functional liver tissue remaining to meet the body’s needs. Your vet will be able to explain in more detail which type of liver disease your pet has been diagnosed with, and what to expect.