Portosystemic Vascular Shunts
How Bile is Made
Dog Liver, Gallbladder, and Pancreas
THE EMMA PROJECT: MICROVASCULAR DYSPLASIA AND WHAT IT MEANS FOR OUR BREED by Christine Dresser D.V.M.
If you attended the PDCA. annual meeting in San Jose in 2012, you heard me discuss our recent experience with dogs who are affected with a form of liver shunt called Microvascular Dysplasia (MVD). I wrote a small article for The Bulletin, but would like to provide a more in-depth look at the subject.
Many breeders and owners are familiar with intrahepatic (inside the liver) portosystemic vascular anomalies (PSVA). In this disease, there are one or more blood vessels that shunt blood around the liver instead of having it go through the liver to have toxins removed. It is considered a genetic condition. Dogs who have these shunts can have no symptoms if their shunts are small, but they can also present with a large range of clinical signs, including seizures or abnormal behavior( especially after eating), vomiting, diarrhea or constipation, drinking and urinating more, drooling, fever and even coma. Surgical ligation of the shunts has long been the gold standard of treatment,however, many dogs can be managed conservatively with diet and medications.
There is a low incidence of dogs with PSVA which may be due to it being a lethal trait in full expression or penetrance. It may result in fetal resorption and small litter sizes. This is not the case for MVD, which has a much higher occurrence rate (perhaps up to 80%) but is generally found by chance, as the vast majority of dogs that have it are clinically normal and have lesions that are non-progressive.
The start of our interest and research on MVD centers around a fawn girl we placed in a wonderful pet home. As I mentioned at the national, her name was Emma and her new mom, Sarah, was a devoted Pug lover with a very keen interest in health, heightened by losing her first Pug to a brain tumor at a very young age. When it came time for Emma’s spay, pre-op blood was done and one of her liver enzymes was very mildly elevated on her chemistry profile. The level would have barely gotten my attention, but Sarah elected to wait a month and recheck the values. The second sample was elevated even further, although still far from an alarming number. The vets then ran a paired sample of Bile Acids. This blood test helps determine liver function. You fast your dog for 12 hours and a sample is drawn (called pre-prandial). The dog then eats a fatty meal and a second sample is drawn 2 hours later (called post-prandial). Emma’s bile acids were elevated indicating a problem with her liver. Sarah and the attending vets decided to schedule the spay, adjust their anesthetic protocol and do a liver biopsy along with the spay. On an interesting note, a third chemistry profile was done the day of surgery and it was all normal. Emma came through surgery fine but her liver biopsy showed she had MVD. We were so surprised, since we have never had a shunt puppy, Emma’s relatives are all robust and healthy, and Emma herself is crazy and off-the-wall and has earned the nickname “Crack Pug”. I tested Emma’s half-brother and his bile acid tests were high. We started expanding our database to include all the dogs residing with us and any we had placed that we could persuade the owners to have done. After a little over 1 month, we had blood tests and DNA collected on 30 dogs, 11 of whom had abnormal bile acids.
I started thinking back to a black bitch I purchased in the 90’s. She developed severe demodex and I treated her with Amitraz dip. She reacted very badly and was comatose for over 24 hours. She did recover. I did not think she would make a good show or breeding candidate due to her health issues and placed her with a friend. As an older dog, she developed health issues and one of the things they looked at was her liver. She had high bile acids and her liver biopsy showed MVD. It is apparent that this is not a new issue facing our breed and it is very much underdiagnosed since the majority of dogs that have it have no clinical issues.
Since the affected dogs are not clinically sick, why should you care if your dogs have this? We have gotten to this point of having 30 to 80% of our dogs affected through the innocent selection of asymptomatic MVD dogs as foundation breeding stock. It is genetically related to the more severe form of shunts and the two forms can occur in the same dog. While the MVD dogs are not “sick”, they can have trouble metabolizing common drugs in something known as the first pass effect. This was the case with the black girl I had purchased and her response to the mite dip. Her body was not able to metabolize a fairly safe dip because of her MVD. Other things that can cause trouble for MVD dogs include anesthesia agents, antibiotics, non-steroidal anti-inflammatories and vaccines. We all know or have Pugs who react badly to vaccines or do not come out of a routine anesthetic event as planned. Knowing ahead of time that you have an affected dog may help you and your vet modify medications so they are less likely to cause adverse reactions in your dog.
Knowing early on that you have a dog with high bile acids caused by MVD can prove helpful in later life if the dog becomes ill and needs a medical workup. Discovering high bile acids when a dog is sick will likely lead to more testing that might not be necessary to determine if a shunt is to blame. If the dog has mild elevations that have been known about for years and have not caused medical problems, they are less likely to be related to any current illness. Bile acids can be run on puppies as early as 4 to 6 months of age. Ideally, paired samples should be done, but information can also be gained by doing just the 2 hour post-feeding sample. The test needs to be sent by your vet to an outside lab, as the in-house test kits are not accurate enough to be of benefit in this screening.
A huge portion about what is known about shunts and MVD is based on the work of Dr. Sharon Center at Cornell University and I have been fortunate enough to read some of her research papers, correspond with her and talk to her. Much of her focus has been on the small terrier breeds that are so often affected, such as Cairns and Yorkies, but Pugs are among the high risk breeds that Dr. Center is looking at. Our club helped sponsor a project she did in conjunction with the Canine Health Foundation. Dr. Center is doing D.N.A. analysis on the high risk breeds and is determined to find the genetic mutation responsible for PSVA and MVD. Her research efforts could be greatly helped if Pug owners with a dog that actually had a portosystemic shunt could submit bile acid tests and D.N.A. on that dog and any relatives that could be collected. Getting samples of relatives is called a kindred sample and is critical to this phase of her work.
In summary, there is a high incidence of Microvascular Dysplasia in Pugs and a lesser incidence of the more serious Portosystemic Vascular Anomalies, the MVD dogs generally have no symptoms and need no special food or medications, screening breeding stock and puppies will help in adjustments of medications and anesthesia and provide a base should more extensive testing due to illness occur later in life, the Bile Acid tests must be run by an outside lab and the D.N.A. research on these disorders is ongoing. Any help with specimen submission would benefit our breed tremendously.
Thank you to Curtis Rowe for his dedication to our breed and his willingness to spend the time and money needed to investigate health issues and openly discuss them so other Pug fanciers and breeders may benefit from our efforts to improve the health and longevity of our breed. Thank you to Dr. Sharon Center for her help and assistance and her lifelong commitment to the study of liver disease in companion animals. Finally, to Sarah and Dave, without whom this problem would have stayed under our radar, thanks for digging in, insisting on turning over every stone and providing a fantastic home and wonderful life for Emma the Crack Pug and her sister, Ch. Lolo.
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Dr. Christine Dresser, DVM
Dr. Christine Dresser, DVM