"The Pathway for Future Generations"

PORTAL SHUNT (LIVER SHUNT)

This condition is often referred to as a "liver shunt" but the current favored term appears to be portosystemic shunt. These have also been referred to by more exact terms since there are specific types of shunts that vary slightly.
 
There are three shunt types: intrahepatic, extrahepatic, or microvascular. The most common is Portosystemic shunt (PSS) occurs in many dog breeds the Yorkshire Terrier is one. It is an abnormal flow of blood between the liver and the body. Since the liver is responsible for detoxifying the body, metabolizing nutrients and eliminating drugs, the blood bypassing the liver can cause indications of a possible PSS which might include, but are not limited to, neurobehavioral abnormalities, anorexia, hypoglycemia, intermittent gastrointestinal symptoms, urinary tract problems, drug intolerance, unthriftiness and stunted growth.

Signs of PSS usually appear before two years of age, but later onset has been recorded. If an animal has a confirmed PSS, corrective surgery can be helpful in the long-term management of these animals. Dietary manipulation is also important in maintaining PSS animals. Mode of inheritance has not been established.

Symptoms:

 
Most shunts cause recognizable 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 & time of onset for the 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
* pushing the head against a solid object
* seizures
* weakness
* salivation
* vomiting
* poor appetite
* increased drinking and urinating
* balance problems
* frequent urinary tract disease or early onset of bladder stones.
* If these signs increase dramatically after eating, it is a strong supportive sign of a portosystemic shunt.

Most dogs will be diagnosed with port-systemic shunts under one year of age, but dogs as old as eight have been diagnosed with the condition. Animals are usually stunted, thin, depressed, have trouble gaining weight, and are usually characterized by the owners as chronic "poor doers". In most affected dogs there will be some degree of behavioral signs ranging from listlessness, apathy, or depression to more severe signs of circling, head pressing, stupor, drooling, blindness, or convulsions, some leading to coma.

These behavioral changes are due to an accumulation of toxins (especially ammonia) that affect the brain causing a condition called Hepatic Encephalopathy. These toxins are most abundant in the blood stream following the dog eating, especially a high protein meal, and may remain high for hours afterward. Not all dogs with the shunt will show this meal associated behavioral change, but in 25% of the affected dogs that do, the diagnosis becomes clearer. A high percent of affected animals show an intolerance to anesthetics or tranquilizers, and will show increased recovery times following use of these products. Even anti-convulsants used to control seizures may be potentially dangerous if allowed to concentrate in a dog with functional shunt.

Approximately 75% of affected individuals will show digestive system symptoms including poor appetite, ascites, vomiting, drooling, diarrhea, or occasionally deranged appetite (eating paper, etc.). Urinary system symptoms may include increased thirst and urination, & in a majority of porto-systemic shunt cases, there will be crystals or stones formed in the urinary tract. These crystals will be either uric acid or ammonium urate (ammonium biurate or thorn-apple crystals.). There can be bladder stones formed or crystals may be noted on the hair around the prepuce or vulva.

* In virtually all porto-systemic shunts there will be a significant rise in the bile acid levels over normal. The use of bile acids in screening clinically normal dogs for liver shunts is not currently being advised due to the variation of normal bile acid levels in Yorkshire Terriers, and other breeds as well.

* Routine performed serum chemistries are fairly nonspecific toward confirming the diagnosis of porto-systemic shunts, but there may be a decreased total protein (primarily albumin), decreased blood glucose, decreased cholesterol, and decreased blood urea nitrogen (BUN). The uric acid levels may be elevated in a significant number of affected individuals. Acid levels are extremely important in the diagnostic screening of symptomatic potential shunts. Fasting and 2-hr. post meal blood samples are evaluated for bile acid levels.
 
* Liver function testing with Bromosulfaphthalein (BSP) or ammonia tolerance testing are sensitive and reliable if performed correctly. These tests measure the liver's ability to excrete/detoxify known agents, and thus measure liver function accurately.

* Radiography. Radiography is one of the most important methods of establishing a diagnosis of porto systemic shunt, and is currently the only universally accepted method of confirming a shunt, short of major surgery. Injection of a radiopaque dye into the spleen (Splenoportograpy) will show the shunt on radiographs and allow accurate assessment for surgical correction.
 
* Nuclear Medicine. The placement of a radiopharmaceutical agent (radioisotope) specific for the liver into the colon for absorption through the mucosa has been gaining favor because of its noninvasive diagnostic value. This procedure requires expensive equipment and the diagnosis is based on the distribution of the radionuclide in the lung or heart compared to that in the liver. This procedure also does not identify the exact location of the shunt for surgical correction if required.
 
* Until recently, ultrasound was fairly unreliable for nonsurgical diagnosis of porto-systemic shunts. With the advent of Color Flow Ultrasound, there is the potential for diagnosis of this condition on non-anesthetized animals. At the present time, this technology appears to be the diagnostic procedure of choice. If currently undertaken research confirms its value, Color Doppler Ultrasound will soon be the preferred screening and diagnostic tool. At the present time, Hepatic Porto-Systemic shunts are considered to be UNQUESTIONABLY genetic by some of the leading canine experts, but the mode has not been identified at the present time; research is being conducted at Michigan State University to identify this pattern (See the Yorkshire Terrier Foundation page and the Joint Research Project between the YTCA Foundation and the CTCA Foundation).

Genetic disorders in dogs can spread relatively rapidly if a dog, whether affected or a carrier, is a well-respected animal in either conformation or ability, and is used extensively for breeding. This is especially true in the case of the male that can produce hundreds of offspring during his breeding life. If the cause of such a condition can be discovered, then a working strategy can be implemented to control and eliminate the disorder. The Yorkshire Terrier Club of America Foundation, Inc. is currently funding research into both the genetic nature of the problem and into the use of Color Flow Doppler Ultrasound as a diagnostic & screening tool.

Inheritance: Unknown, assumed to be polygentic recessive

For permission to reproduce this article, please contact Dr. Bell:  jerold.bell@tufts.edu