The liver is an important organ, responsible for breakdown of nutrients and for the synthesis of many molecules such as albumin,
coagulation factors, cholesterol, glucose, and many others. The liver has an enormous regenerative capacity. For example,
in humans half of a liver can be transplanted from a living donor to a recipient and within 6 weeks both the transplanted
liver and the remaining liver of the donor will reach a hepatic volume. Despite its regenerative capacity liver disease can
lead to death as the body cannot survive without the liver and exogenous support of hepatic function in dogs and cats is currently
not possible, even in the short-term. Liver disease is common in both dogs and cats. Acute liver disease can be caused by
infectious diseases or intoxications. Chronic liver disease occurs much more commonly than acute liver disease. The most common
chronic hepatic diseases are chronic hepatitis or cholangitis, copper-associated hepatopathies, iatrogenic liver disease,
and hepatic vascular disorders, which, with the exception of hepatic vascular disorders, will be discussed in more detail
in the following.
Chronic hepatitis and cholangitis
Chronic hepatitis is a heterogeneous group of chronic liver diseases in the dog that are associated with an inflammatory infiltration
of the liver. Similarly, cholangitis is a heterogeneous group of diseases of the liver and biliary tract in cats that all
lead to inflammatory infiltration of the liver and the biliary tract. There are many different etiologies of chronic hepatitis/cholangitis,
including infectious (e.g. infectious canine hepatitis or leptospirosis), drug-induced (e.g. anticonvulsants), familial-predisposition
(e.g. in the Doberman pincher, Bedlington terrier, Cocker Spaniel, West Highland White terrier, and others). However, most
cases of chronic hepatitis/cholangitis are idiopathic.
Clinical signs in dogs and cats with chronic hepatitis/cholangitis are often non-specific. Lethargy, anorexia, weight loss,
and vomiting are most common. Cats with cholangitis may also show fever and abdominal pain. Other signs such as diarrhea,
polydipsia, polyuria, icterus, ascites, and bleeding diathesis may also be seen when the liver is failing.
The most common findings in dogs and cats with chronic hepatitis/cholangitis are an increase in liver enzymes, such as ALT
and SAP. In more severe cases hypoalbuminemia, hyperbilirubinemia, hypocholesterolemia, and a decrease in BUN may also be
observed. Approximately half of all cats with cholangitis have hyperglobulinemia but this is not a common feature in dogs
with chronic hepatitis. Fasting and post-prandial bile acid concentrations may be increased depending on the severity of the
disease process. In patients with hepatic failure coagulation parameters may be abnormal either due to lack of synthesis of
coagulation factors or due to disseminated intravascular coagulation.
Abdominal radiographs are usually within normal limits. However, in patients with end-stage cirrhosis the liver may appear
small. Abdominal ultrasound often reveals changes in hepatic echogenicity and irregular hepatic margins. In more severe cases
ascites and acquired intrahepatic shunts may be visualized.
A diagnosis of chronic hepatitis/cholangitis is based on histopathology. Cytological evaluation of a fine needle aspirate
is not sufficient for diagnosis of chronic hepatitis/cholangitis. Biopsy samples for histopathology can be collected by true-cut
biopsy, laparoscopy, or exploratory laparotomy. True-cut biopsy is least invasive but only allows for collection of small
biopsy samples. In contrast laparoscopy allows for collection of much bigger samples and allows for visual inspection of the
liver surface and also for direct control of bleeding. One study has suggested that biopsy by laparoscopy is superior to true-cut
biopsy. However, more studies are needed in order to make a conclusive assessment. Regardless of the way the biopsy is collected
one biopsy sample should always be submitted for bacteriologic culture.