Liver Disease

Liver Function

The liver is the largest organ in the body.  It has 6 distinct lobes organized into three regions.  The healthy liver only uses a small amount of it's full potential at any one time.  Unfortunately, because of this reserve power, diseases of the liver are often not diagnosed until the disease is significantly advanced.  On a positive note, liver cells can regenerate themselves.  This regeneration ability allows a diseased liver to return to normal function in some cases.

Some of the liver's functions are:

Causes of Liver Disease

Symptoms of Liver Disease

The symptoms of liver disease are variable and are normally very subtle in the early stages of liver problems.  Some dogs show no symptoms early in the course of the disease.  The classic symptoms are:

Poor Appetite

Weight loss

Excessive thirst and urination

Lethargy

Anemia

Light colored  or abnormal colored stool

Bleeding disorders

Distended abdomen

Vomiting, nausea or diarrhea

Orange colored urine or mucous membranes due to jaundice

Behavioral changes - circling, head tilt and seizures.

 

Portosystemic Shunt (PSS)

Portosystemic shunts are abnormal vascular connections between the vein that connects the gastrointestinal tract with the liver (portal vein) and the vein that carries blood back to the heart (posterior vena cava). A liver shunt causes the blood in the gastrointestinal system to be diverted past the liver where it would normally be detoxified before being sent to the rest of the body. 

Ammonia comes from bacteria in the intestines and when muscles utilize protein as an energy source.  In a normal dog this ammonia gets delivered through the portal vein directly into the liver.  The liver metabolizes the ammonia to urea, which is then excreted by the kidneys.  The liver also detoxifies bacteria and drugs when they are absorbed from the intestines before they get into general circulation.  When a liver shunt is causing blood to by-pass the liver, toxins that are normally metabolized by the liver (especially ammonia) are allowed to enter the general circulation before being detoxified.  It's the ammonia buildup that causes most of the symptoms associated with PSS.  A dog may develop hepatic encephalopathy because of the toxic effects on the brain. 

Shunts can be multiple or single and they can be intrahepatic (within the liver) or extrahepatic (in the blood supply before it enters the liver).  Microvascular dysplasia is an unusual form of intrahepatic shunt in which no gross vascular abnormality can be identified.  This rare condition is associated with somewhat milder clinical signs.

Most portosystemic shunts are congenital, although they may be acquired secondary to liver disease.  The prevalence of congenital portosystemic shunts in certain breeds suggests an inherited predisposition.  Breeds that are predisposed include Irish wolfhounds, Maltese, Yorkshire terriers, Miniature schnauzers, Australian cattle dogs, Retrievers, Cairn terriers and Old English sheepdogs.

The symptoms of a PSS are usually present by the time a dog is six months old but may not be recognized until middle age.  Symptoms include depression, seizures, loss of muscle control, vomiting, excessive thirst and urination and stunted growth.

Medications and diet may be helpful, however, surgery to close off the shunt is the only way to totally eliminate the problem.   Non-surgical treatment may include:

Dietary Modification - A diet that is restricted in protein may be beneficial because less ammonia is produced as a by-product of metabolism.  The protein needs to be of high biological value such as eggs and dairy products.  Meat based proteins should be avoided since they increase the chance of hepatic encephalopathy.

Lactulose - Lactulose works in the large intestine to minimize the production of ammonia by bacteria.

Antibiotics - These drugs are given to minimize the bacteria count in the colon.

Chronic Active Hepatitis

Chronic active hepatitis is a series of different liver diseases with similar characteristics when analyzed under the microscope.   Hepatitis is an inflammation of the liver that can be caused by an infection, drugs like Phenobarbital, trauma, bacteria and toxins.  As hepatitis progresses, normal liver cells are replaced with fibrous tissue.  Eventually the blood flow through the liver is compromised.  After a variable period of time liver failure often develops.

The treatment of chronic active hepatitis starts with eliminating the offending drug or toxin if it's known.  Antibiotics that have minimal need for liver metabolism are used to control bacterial infections.  Dietary modification would include a diet restricted in protein.  The protein needs to be of high biological value such as eggs and dairy products.  Meat based proteins should be avoided since they may increase the chance of hepatic encephalopathy.  Ulcer medications may make a dog more comfortable and more inclined to eat.  Additional liver specific drugs may be used.  Corticosteroids are used if there is evidence that the immune system is implicated as a cause of the liver disease.  Ursodiol replaces toxic bile acids with a type of bile that is less toxic.  Milk Thistle a natural supplement may be used to stimulate the liver to produce new cells.

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Last Updated August 2009