[megansmomma]

Cont.

Surgery
Most dogs are taken to surgery to have the shunt closed. Because the liver has not developed properly, many dogs cannot 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".
Latest Update 2002
As many of you know, I have been completing a study funded by the AKC Canine Health Foundation regarding determination of genetic relationships among Yorkshire Terriers with single congenital portosystemic shunts. Our objectives were to determine whether coefficient of inbreeding was greater in Yorkies with portosystemic shunts (PSS) than Yorkies with normal bile acids (NBA) and to determine whether a common ancestor was present in the pedigrees of dogs with PSS. We excluded pedigrees of full siblings from our analyses so that a wide variety of breedings would be included. Pedigrees were entered into a data collecting system (“The Breeder’s Standard”; Man’s Best Friend Software, Version 5.0.632, 1999). Wright’s coefficient of inbreeding for up to 10 generations was calculated for each dog. Five and eight generation pedigrees were analyzed for common ancestors.

We found that the Wright’s coefficient of inbreeding for Yorkies with single congenital extrahepatic portosystemic shunts was twice as high as that of Yorkies with normal bile acids (0.054 +/- 0.094 and 0.028 +/- 0.042, respectively). This difference was not statistically significant, however; we would need to study the a greater number of pedigrees with PSS to see whether inbreeding was a factor in shunt development in Yorkies, as it is in Irish wolfhounds.
We evaluated the pedigrees for common ancestors and, in the PSS group, found one dog that was mentioned repeatedly in most the five and 8 generation pedigrees. However, this dog was also mentioned in most of the pedigrees of the normal Yorkies as well, and therefore cannot be implicated in the disease.
Bottom line: The news is good and bad. For those folks that are concerned about a certain dog or dogs in their lines, there is no proof that a single dog or line is the source of the disease. I'm sure that is a relief for many breeders. However, it would have been much easier to find out that a certain dog or line was responsible, as that would make the problem easier to avoid. Based on our results, the trait is likely to be polygeneic; thus, there is no easy answer as to how to avoid the disease. Veterinarians will likely continue to recommend that neither parent of a shunt dog be bred again or, at the very least, that test breedings of parent to offspring be performed to rule out carriers. Research is now underway at Ohio State University and Michigan to look for a genetic marker. If you know of anyone that has 2 affected dogs in the same line, please contact us or any of the involved Universities. Your information may provide the key to developing a test that will save future generations from this disease.
You are welcome to forward this information to other listservs and internet sites. I'm happy to answer any questions about the study or about shunts.
Karen Tobias DVM MS ACVS
University of Tennessee
Department of Small Animal Clinical Sciences
P.O. Box 1071
Knoxville TN 37901-1071