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Portosystemic Shunts : Can We Talk ?

By Karen M. Tobias

DVM, MS, Diplomate American College of Veterinary Surgeons Associate Professor, 

Small Animal Surgery, University of Tennessee Department of Small Animal Clinical Sciences

   

Introduction

Portosystemic shunts are a common topic of conversation amongst breeders and owners of small and toy breed dogs. 

Congenital portosystemic shunts are being diagnosed with increasing frequency, and many breeders and

veterinarians are questioning whether heredity may play a role in the spread of this disease

  

What are Portosystemic Shunts ?

A portosystemic shunt is a blood vessel that bypasses liver tissue, carrying blood from the intestines, stomach, spleen,

and pancreas to the heart before it can be filtered and cleansed of proteins, sugars, bacteria, and toxins.
Shunts are present in all fetal mammals and usually close down shortly before or after birth so that the baby's liver

takes over the functions of filtration, storage, and production.  In some individuals the shunt doesn't close

down or develops in an abnormal place, and the animal's liver doesn't get enough blood supply to grow or function

properly

  

Types of Shunts:

Shunts may be congenital (found at birth) or acquired (developing after birth). Dogs with acquired shunts usually have

cirrhosis, or "hardening" of the liver, secondary to severe liver disease. These dogs develop multiple shunting

blood vessels to relieve high blood pressure in the liver.

 

There is no effective surgical treatment for these patients, short of a liver transplantation. Congenital shunts are  

usually single blood vessels that are present at birth. In large breed dogs, they are found inside of the liver

( "intrahepatic" ) and may be a result of improper or incomplete closure of the fetal shunt.

 

Surgical treatment of these shunts is possible, but difficult, because of the location of the abnormal blood vessel. 

Small and toy breed dogs usually have "extrahepatic" shunts: the blood vessel is located outside of the liver. These

shunts are easier to find and treat and therefore the outcome of surgery is better 

Clinical Signs of Portosystemic Shunts

Clinical signs are often seen at a young age and may include poor growth, behavioral changes ( circling,

disorientation, unresponsiveness, staring into space, head pressing, blind staggers), seizures, and quiet demeanor.

Many of the clinical signs may be confused with puppy hypoglycemia (low blood sugar). Other less common signs

include drinking or urinating too much, diarrhea, and vomiting.

In many animals the signs are seen 1-3 hours after eating meat or puppy chow. Proteins in the food are broken down

by intestinal bacteria to ammonia and other toxins, which are absorbed and, instead of being filtered by the liver,

are allowed to reach the brain. The depression and signs are often temporary; once the proteins are emptied from

the colon, the signs usually abate. Some animals may not show clinical signs until they are anesthetized to be

castrated or spayed.

These animals may take days to recover from anesthesia, depending on what drugs were used. Other animals show

no signs until they are older, when they develop bladder and kidney problems from excreting toxins and forming

crystals and stones.

  

Diagnosis

To diagnose a shunt we may need to rule out toxicity, hydrocephalus ("water on the brain"), and low blood sugar in

puppies. We look for abnormalities on bloodwork that indicate poor liver function, such as low protein, albumin, and

blood urea nitrogen, which are chemicals produced by the liver. X-rays of the abdomen may show a small liver,

indicating that it is has not developed properly.

Urine sediment may contain ammonium biurate crystals, which look like starfish or spiky balls. We also run special

diagnostic tests. Blood ammonia concentration can be measured; this test will diagnose liver disease in 90% of

affected animals. It is more accurate (95 to 100%) if an ammonia challenge is done, where the puppy is given

ammonia per rectum or orally and the blood is tested to see if the liver clears the ammonia.

Blood for ammonia concentration measurements must be kept chilled and must be analyzed within 30 minutes after it

was drawn. Even more accurate are bile acid concentrations. A blood sample is taken after a 12 hour fast, and then

the puppy is fed a normal meal. Two hours later another blood sample is taken. Bile acid concentrations are high in

most types of liver disease, including shunts. Bile acid concentrations are altered by hemolysis (breakage of the blood

cells) and lipemia (fat in the blood) but are minimally affected by temperature and storage and can be sent through

the mail.

These tests tell us that liver disease is present but do not verify the presence of a shunt. Bile acids levels that are

normal in a 6 or 8 week old puppy indicate the puppy probably does not have a shunt, as long as there is no hemolysis

of the blood sample; therefore this test can be a good screening tool for breeders.

To be 100% sure that a shunt is present, we either need to use ultrasound (which is more useful in large dogs), 

a contrast study with x-rays ("portogram"), nuclear scans ("scintigraphy"), or surgery to find the shunt. Scintigraphy 

and ultrasound are not invasive and are therefore the safest tests, with scintigraphy being the more accurate of the

two. Portosystemic shunts must be differentiated from hepatic microvascular dysplasia, a disease that has the same

clinical signs, liver biopsy results, and blood changes. This disease is seen in Yorkies, Cairn terriers, and other small

breeds and must be ruled out by portogram or scintigraphy.

    

Medical Treatment

Dogs with shunts that are seizuring or comatose should be given intravenous fluids with dextrose (sugar),

intravenous antibiotics, and warm water enemas. Lactulose syrup can be instilled in the rectum after the enema to

decrease toxin absorption.

Some dogs may even need activated charcoal (given by tube through the mouth into the stomach) to absorb toxins 

if they are comatose. Long-term medical treatment for dogs with shunts includes a low protein diet such as 

Hill's L/D, and drugs such as lactulose and neomycin or metronidazole to prevent production and absorption of

ammonia and other intestinal toxins.

Lactulose, a sugar solution, is extremely safe, although a high dose will cause diarrhea. Some animals do well 

on medical treatment alone, but most have a shortened life span because of progressive liver shrinkage and loss 

of function. Medical treatment is normally used to stabilize a patient until it is healthy enough to 

tolerate the surgery.

   

Surgery

Most dogs are taken to surgery to have the shunt closed. Because the liver has not developed properly, many dogs can

not tolerate rapid closure of the shunt. Some veterinarians will partially occlude the vessel, 

leaving a small amount of shunting present.

Many of these dogs still do well after surgery and about half are able to be taken off of medication and special diets

within 6 months. In some, the clinical signs may recur, and a second surgery may be required to determine 

whether further closure can be attempted.

Many veterinarians are now placing ameroid constrictors around the shunts to gradually occlude them. 

These constrictor rings will slowly close down over 4-5 weeks, allowing the liver to get used to its new blood supply.

Survival rates after ameroid constrictor placement are about 95 %.

Most dogs are completely normal within 3 months. While about 1/3 of the dogs may still have some shunting, 

less than 15% have any clinical problems.

     

Postoperative Management

Most dogs will need to be kept on a low protein diet for at least 6 weeks after surgery. 

Liver function can be assessed at 2-3 months by rechecking albumin and postprandial bile acids, or by scintigraphy.

Dogs can be gradually switched to an adult maintenance diet after 8 weeks, 

but should be kept on a low protein diet and lactulose if clinical signs recur.

  

Prevention

Portosystemic shunts have been proven to be hereditary in Irish Wolfhounds and Maltese; however, 

we also see them frequently in other breeds such as Yorkies, Australian shepherds, and Labrador retrievers.

Currently I am investigating the pedigrees of Yorkshire terriers, since the odds of this breed developing shunts 

are 1,225 times greater than all other breeds combined.

At University of Tennessee Veterinary Teaching Hospital, 35% of our shunt patients are Yorkies ; 

at Washington State University, one out of seven Yorkshire Terriers presented to Veterinary Hospital for any reason

was found to have a portosystemic shunt. Because of the high prevalence of the disease in Yorkies, 

we are determined to search for the cause and to look for a "cure."

  

Papillons and Shunts

While Papillons with shunts as not as common as Yorkies, they have a greater risk for the disease than the general

canine population. Papillon breeders are in an enviable position - the incidence of the disease is still relatively low, 

the veterinarians are now more aware of how to diagnose and treat it, and the dialog concerning shunts is 

still fairly open. If ignored, portosystemic shunts may rapidly spread through the population 

until no one's breeding program is safe.

   

What Can You Do to Help ?

If one of your dogs or its offspring has had a portosystemic shunt, send the pedigree and the name, 

address, and phone number of the veterinarian that diagnosed the shunt to me at the following address :

    

Dr. Karen Tobias
University of Tennessee
Department of Small Animal Clinical Sciences
PO Box 1071
Knoxville, Tennessee 37901-1071.

  

Alternatively, the information can be faxed ( 865-974-5554 )

Information will be kept confidential; names of breeders, owners, and dogs will not be published.

If you or someone you know has had a dog or lineage that has produced several puppies with shunts, 

please contact us ! We may be able to evaluate the pedigrees and blood work of these dogs and their close kin to 

solve the entire question of heredity.

Contact me confidentially, and I will explain to you how this can be done. Remember, articles on genetics use circles

and squares to represent the animals- never names.

It is my sincere hope that Papillons can avoid the plight of Yorkshire Terriers. 

Let's see if we can solve this problem together.

 
 

Note: This article was obtained for Pap Talk by the PCA Genetic Disorders Committee. 

It is the author's summary of a seminar she conducted at the PCA National Specialty.

 

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