Liver Shunt
(Portosystemic Shunt)
Under normal circumstances, blood passes through the liver to be detoxified. When one eats, many by-products of digestion are formed in the blood -- some of these by-products are beneficial, but some are not. Amongst the liver's many functions is its role in detoxifying the blood of the bad by-products -- excess bile acids, ammonia, and other substances. In Portosystemic Shunt, the blood that would normally go to the liver to be detoxified bypasses the liver. Toxins build up in the blood and affect the brain, which leads to changes in behavior and severe lethargy, depression, and weakness. Seizures often occur as well
Portosystemic shunts are a congenital problem that can be seen in some Maltese. During gestation the placenta delivers blood with food and oxygen from the mother through the umbilical vein. This means that in the fetus, circulation is the reverse of circulation after birth, because the fetus' veins have the oxygenated blood and arteries return unoxygentated blood to the heart. In order to make this work, there is a shunt from the liver venous circulation to the arterial circulation. At birth, the pressure within the circulatory system changes as respiration occurs and this closes the shunt, which eventually disappears. If this reverse in circulation does not happen for some reason, the liver is deprived of a blood supply and does not develop properly after birth. Many puppies can live with the small functioning portion of the liver for some time but eventually have problems and usually die if the situation is uncorrected.
Most shunts cause recognizable clinical signs by the time a dog is a young adult but once in a while one is diagnosed at a later time in life. Since the severity of the condition can vary widely depending on how much blood flow is diverted past the liver it is possible for a lot of variation in clinical signs and time of onset of signs to occur. Often, this condition is recognized after a puppy fails to grow, making an early diagnosis pretty common.
Signs of Portosystemic Shunts include poor weight gain, sensitivity to sedatives (especially diazepam), depression, head pressing (pushing the head against a solid object), seizures, weakness, salivation, vomiting, poor appetite, increased drinking and urinating, balance problems and frequent urinary tract disease or early onset of bladder stones. If the signs of problems increase dramatically after eating this is a strong supportive sign of a Portosystemic Shunt.
There is not an easy test to diagnose Portosystemic Shunts. Special dyes can be injected into the liver circulation that show up on X-rays can outline the problem pretty clearly most of the time. But this is a pretty invasive test making it a poor choice for "screening" purposes. There are a number of possible abnormalities that might point towards a portosystemic shunt on routine labwork, including low BUN (blood urea nitrogen), low albumin, mild anemia, increases in ALT (serum alanine aminotransferase) or ALKP (serum alkaline phosphatase). If these signs are present, it would be a good idea to test the serum bile acid levels prior to eating and after eating. This test is supportive of poor liver function. If these tests are abnormal it may be a good idea to consider an ultrasound and dye contrast X-rays.
The therapy for PSS is multifaceted. The initial step is to feed the animal a special low-protein diet. Low protein diets decrease the amount of ammonia produced during their metabolism. Often, the diet includes lactose to bind the ammonia produced by the normal bacterial flora in the bowel. Antibiotics (metronidazole usually) are sometimes administered to eradicate the ammonia-producing bacteria in the bowel.
Ultimately, you can have further diagnostic tests performed to determine if the shunt can be repaired surgically. An ultrasound of the liver can be performed to assess the vasculature. In some institutions, special dye studies can be performed to confirm the shunt. A biopsy of the liver is not needed and does not give the veterinarian any more information.
In almost all cases, surgery is recommended. As you can imagine, there are risks with such a surgery and the recovery must be in intensive care. A Maltese owner faced with Portosystemic Shunt should see a Board-certified veterinary surgeon to discuss the procedure at length.
