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Liver Shunt and the Yorkshire Terrier
DEFINITION AND TYPES
 


“ Portosystemic shunts are abnormal vascular connections between the hepatic portal vein (the blood vessel that connects the gastrointestinal tract with the liver) and the systemic circulation. Such anomalies cause blood in the gastrointestinal track to be diverted past the liver, there by limiting the liver’s vital functions, in metabolism and detoxification of compounds and the body’s defenses against intestinally derived pathogens. This effectively exposes the body to toxic by-products of digestion (toxins and bacteria) and mimics the effects of liver failure.”

T.D.G. Watson, BVM&S, PhD, MRCVS
Waltham Center, United Kingdom

Portosystemic Shunts (PSS) can be classified as Extrahepatic (outside the liver) or Intrahepatic (inside the liver), single or multiple, congenital or acquired.

Extrahepatic Shunts are most common and constitute over 60% of all congenital shunts. Extrahepatic Shunts tend to be found more commonly in small breed dogs, such as Yorkshire Terriers, Maltese, Dachshunds, and Schnauzers. Of these, the Yorkie is 36 times more likely to have congenital Extrahepatic shunts than the other breeds.

Intrahepatic Shunts account for less than 40% of all congenital shunts is more often seen in large breed dogs, such as Irish Wolfhounds and Golden Retrievers. Within the first three days of life the natural opening of the embryonic connection closes. In Intrahepatic Shunts dogs the embryonic connection remains open.

Multiple Acquired Shunts are a result of an increase in liver pressure. This can be a result of the surgical closing of an Extrahepatic Shunt in surgery. Multiple Acquired Shunts are not surgically correctable.





 
CLINICAL SINGS OF LIVER SHUNT
 
Dogs with PSS are usually purebred and less than a year old when signs first develop. Poor coat development, lethargy, long sedation recovery, Urinary Tract Infections, disorientation, head pressing, anorexia, depression, weakness, excessive salivating, and temporary blindness have all been connected with Liver Shunt. Vomiting and diarrhea are reported in roughly two-thirds of Liver Shunt cases and in older dogs. Less common signs are recurrent fevers and ascites. Ascites is usually associated only with Acquired Shunts.
 



 
DIAGNOSIS OF LIVER SHUNT
 
In identifying Liver Shunt the identity of the anatomical location of the shunt, its severity, and whether the shunt is congenital or acquired need to be determined. Different Veterinarians utilize different methods for these procedures.

Initially a round of blood work is usually ordered. Common blood work orders are: a full blood chemistry panel, a hematology panel, and a liver profile. It is the combination of elevated liver enzymes combined with low serum cholesterol, hypoglycemia, low blood urea nitrogen, and the total plasma protein concentrations that indicate that a liver shunt is evident.

Serum Bile Acids are also helpful in the making a more definitive overall picture in diagnosing the presence of a Liver Shunt and is usually taken when the blood work is indicative there is a shunt present. It is possible to test the Bile Acids in young puppies. However, unless the puppy is showing apparent signs of PSS a Bile Acid Test can throw false readings. It is recommended an apparently healthy puppy be a minimum of two pounds and 6 to 9 months old to test the Bile Acids accurately.

Once the blood work has been completed multiple testing procedures may take place to help identify the severity and location of the shunt. Three common procedures are: Doppler Ultrasound, Contrast Radiography, and Scintigraphy. Doppler Ultrasound is a 95% accurate and noninvasive procedure for the detection of Portosystemic Shunts.

Contrast Radiography is the application of a dye injected into the blood stream allowing for easy visualization of the location of the portal shunting and is often done in conjunction with surgery so as to minimize anesthesia of the dog. Scintigraphy is the application of radioactive chemicals into the rectum allowing for the diagnosis to the degree of the shunting allowing a more accurate assessment for management options of the disease.
 



 
TREATMENTS AND MANAGEMENT OF LIVER SHUNT
 
Several options exist for dogs diagnosed with Liver Shunt. Many cases can be treated with medical management and diet. Diet is used to limit the production of neurotoxin production in the large intestine thus reducing the stress put on the liver. The limiting of proteins into smaller amounts and only feeding highly digestible sources does this. Protein restricted diets such as Hills, l/d, k/d or Royal Canin Hepatic LS along with lactulose, milk thistle, and occasionally antibiotics are often times successful in treatment of more minor shunt cases.

Surgical options include placements of ameroid constrictors, cellophane bands, and partial suture ligation. 85% of surgical cases of Single Extrahepatic Shunts are successful in the United States. Of the 15% of cases that are not so successful, most are a resulting failure due to either Multiple Acquired Shunts developing from the new pressure being placed on the liver or due to a pre-existing condition such as Hypolatic Microvascular Dysplasia or Portal Atresia.
 



 
HYPOLATIC MICROVASCULAR DYSPLASIA (MVD) / PORTAL ATRESIA (HMD)
 
Hypolatic Microvascular Dysplasia or MVD/HMD is a congenital defect where the portal vein breaks into smaller microscopic vessels in the liver which are poorly formed or undeveloped. This lack of development causes the liver to atrophy which in turn inhibits the liver from filtering out toxins and allowing for normal growth. Dogs can have both a Liver Shunt and MVD/HMD. They can also have one condition without having the other. MVD/HMD livers and shunted liver samples look identical under the microscope and thus can often be misinterpreted for the other. However, a dog with both Liver Shunt and MVD/HMD must have the shunt surgically corrected successfully before a definite conformation of MVD/HMD can be made.

The sign of MVD/HMD are identical to that of Liver Shunt. However, in many cases there are no evident signs of a problem until the dog is 3 to 4 years old. There is currently no treatment for MVD.
 



 
BREEDING THE FUTURE
 
Hopefully, in the future simple blood tests will be able to identify carriers allowing for breeders to eliminate this terrible condition from the Yorkshire Terrier and other dog breeds that are producers of the disease such as Tibetan Spaniels, Cairn Terriers, Havanese, Shih Tzu, and Maltese.

The Yorkshire Terrier Fanciers Foundation is currently working with Dr. Sharon Center, DVM, DiplACVIM, Professor and Internal Medicine Specialist of the department of Clinical Sciences, College of Veterinary Medicine, Cornell University to help provide a base in genotyping Liver Shunt. Dr. Center, as the developer of the Bile Acid Test, believes that Liver Shunt is an ancient mutation in the dog that involves vasculogenesis or angiogenesis (embryologic formation of the blood vessels) and that the need to establish a demonstrated genotype linkage between the breeds is crucial.

The Foundation has provided a letter of intent to the AKC’s CHF in support of a grant proposal for the project. Dr. Center is currently projecting 18-24 months before a DNA Marker test may become a reality.

As with all genetic and congenital defects, dogs with either Liver Shunt or MVD/HMD should not be used for breeding and should be spayed or neutered.

http://www.vet.cornell.edu
http://en.wikipedia.org/wiki/Portosystemic_shunt
http://members.cox.net/jonanyorkies/livershunt.html
http://www.vet.utk.edu/clinical/sacs/calendar
http://www.vetsurgerycentral.com/pss.htm
http://www.vetmed.ufl.edu
 








 
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