The liver plays an important role in carbohydrate, lipid and protein metabolism as well as vitamin and mineral storage. The
liver is also vital in detoxification of metabolic products (ammonia, uric acid), hormones and drugs. There are several diseases
of the liver in the dog that can result in inflammation. The two most common, acute and chronic hepatitis, will be the focus
of this discussion.
There is no age, sex or breed predisposition to acute hepatitis. Breeds with an increased incidence of chronic hepatitis include
the beagle, Bedlington terrier, cocker spaniel, dalmatian, Doberman pinscher, German shepherd dog, Labrador retriever, Scottish
terrier, Skye terrier, standard poodle and West Highland white terrier. Most of these breeds have also been shown to have
increased copper in their liver. Middle aged dogs are more commonly affected with chronic hepatitis and in certain breeds
there is a sex predilection (i.e. female Doberman pinschers, male cocker spaniels).
Acute and chronic hepatitis is often idiopathic but can also occur because of exposure to chemicals, drugs, mycotoxins and
infectious agents. The liver is particularly susceptible to toxic injury because of its rich blood supply that will bring
large quantities of potentially toxic substances to the liver. Infectious diseases such as infectious canine hepatitis and
leptospirosis have also been associated with acute hepatitis and proposed as an etiologic agent for more chronic forms of
hepatitis. Metals such as copper and iron are sometimes increased with more chronic forms of hepatitis. Copper accumulation
as a primary defect is inherited as an autosomal recessive trait in the Bedlington terrier where there is a defect in copper
metabolism in hepatocytes so it is not excreted normally into the bile. As a result, copper gradually accumulates in the hepatocytes
resulting in inflammation. In other breeds reported to have high quantities of copper in their livers (Dalmatian, West Highland
white terrier, Skye terrier, cocker spaniel, Doberman pinscher, Labrador retriever) it is not known whether it is the primary
cause of hepatitis (i.e. some sort of defect leading to accumulation) or the result of secondary damage due to cholestasis
(impaired excretion secondary to underlying liver disease). Iron accumulation is believed to be secondary in hepatitis, but
may contribute to hepatic injury and inflammation. In chronic hepatitis immune dysregulation is suspected to play a role but
whether it is the cause of disease or a response to the inciting event is unknown. The presence of lymphocytes and plasma
cells is fairly common with chronic hepatitis and CD3+ T lymphocytes were the most common lymphoid cell in the liver of a
group of dogs with chronic hepatitis. Antinuclear antibodies and antibodies to hepatocytes have also been found in some dogs
supporting the role of an immune response. There are other systemic inflammatory or infectious diseases that can cause chronic
hepatitis but in most cases the cause is unknown and the term idiopathic is used.
In acute hepatitis the signs tend to be more acute and severe. These animals may present with signs of hepatic encephalopathy
and may be depressed, moribund or comatose and occasionally seizure. Lethargy, anorexia, vomiting and icterus are common.
Fever may occur. Dogs may be dehydrated so mucous membranes may be tacky. Disseminated intravascular collapse (DIC) with petecchia
and other signs of bleeding (hematemesis, melena) may be seen in severely affected cases. There might be pain and hepatomegaly
on abdominal palpation.
In chronic hepatitis, dogs may be normal or present with weight loss, polydipsia, polyuria, intermittent vomiting, diarrhea,
decreased appetite and abdominal distention. Hepatic encephalopathy, icterus and bleeding tendencies are occasionally seen
in more advanced stages but seizures are rare. The liver may be normal or decreased in size in these dogs.