Liver shunts in Norwich terriers

Introduction

A liver shunt is a blood vessel that carries blood around the liver instead of through the liver. Thus blood that would normally be filtered by the liver does not get filtered which allows the build up of toxins in the blood stream. Liver shunts are a polygenetic disease for which we have no DNA test ([1]). It seems to have two forms in small dogs, which are suspected of being genetically related - a mild form called portal vein hypoplasia or microvasular disease (PVH-MVD), and a severe form called a portosystemic shunt (PSS). It is thought that the incidence of PVH-MVD is much higher that PSS, since most dogs with PVH-MVD never show any signs and hence never have their liver tested.

In a population of dogs seen at the UC-Davis Vet Hospital, Norwich terriers were the second most likely breed to have a liver shunt ([2]).

Portal Vein Hypoplasia

An older name for portal vein hypoplasia (PVH) is microvascular disease (MVD). In this form, very small shunts are found throughout the liver. A PVH-MVD dog usually does not show any signs. A bile-acid test (liver function test) usually shows only mildly abnormal values. A special "Protein C" blood test - done only at Cornell - can be used to differentiate between PVH-MVD and PSS ([3]). Most dogs with PVH-MVD live a normal life without any complications from PVH-MVD; however they may have trouble metabolizing drugs that require rapid delivery and extraction in the liver ([4]).

Portosystemic Shunt

A portosystemic shunt (PSS) is sometimes called a portosystemic vascular anomoly (PSVA). In small dogs this is a shunt outside the liver (extra-hepatic shunt). In large dogs, it is typically a shunt inside the liver (intra-hepatic shunt). This is most frequently found when a dog shows signs such as lethargy, a routine blood test points to the liver, then a bile-acid test (liver function test) shows very high abnormal values. Some dogs survive without surgery, but most need surgery.

Liver testing is recommended for all Norwich

Dr. Sharon Center - one the world's leading researchers on canine liver shunts - recommends bile-acid testing of all puppies in breeds affected with liver shunts. ([5]). You can do a bile-acid test on a dog as young as four months old; earlier can give abnormal readings. The purpose is to know a dog's liver status in case of some medical problem later in life. You do not want a vet to be surprised by abnormal bile acids results, which might make the vet suspect and investigate the liver ... rather than concentrating on the actual signs of the medical problem.

A bile-acid test is nothing more that a blood draw ("preprandial" i.e., fasting) followed by a meal, then two hours later another blood draw ("postprandial"). A lab can then analyze the blood and report on the bile acid levels (which indicate liver function).

A compromised liver causes anesthesia risk; some Norwich have died from anesthesia during routine dental exams. Possibly a liver shunt was the cause of death of some of these cases. Since the purpose of the liver is to filter out toxins from the blood, if the liver is not working correctly, it is possible for the dog to have seizures. Idiopothic seizures (seizures of unknown origin) have been reported in Norwich terriers; possibly a liver shunt was the cause of some of these cases. Also "fading puppies" have been noticed by Norwich breeders, again it is possible that the cause is a liver shunt.

Further Information

For further introductory information see references [4], [5], and [6]. For more in-depth information see references [7], [8], [9], [10], [11] and [12].

There is a high message volume Liver_Shunt_And_MVD_Support yahoogroup.

Last updated 10 August 2016.

References

[1] Complex disease and phenotype mapping in the domestic dog Hayward et al., Nature Communications, 22 January 2016.

[2] Prevalence of inherited disorders among mixed-breed and purebred dogs: 27,254 cases (1995-2010), Bellumori et al., JAVMA Vol 242 No 11, June 2013.

[3] Cornell Comparative Coagulation Protein C Web Site.

[4] Help! My Dog was Diagnosed with a Liver Problem!, Dr. Karen Tobias, University of Tennessee College of Veterinary Medicine.

[5] Portosystemic Vascular Malformations in Small Animals, Merck Vet Manual, article by Dr. Sharon Center, last updated May 2015.

[6] Portosystemic Shunts, AKC/CHF web page.

[7] Hepatic Vascular Malformations In Small Dog Breeds: What the Textbooks Don't Tell You, Dr. Sharon Center, 2009.

[8] Medical Management: Portosystemic Vascular Anamalies (PSVA), Dr. Sharon Center, 2011.

[9] Diagnostic Approach: Portosystemic Vascular Anomalies (PSVA), Dr. Sharon Center, 2011.

[10] Inherited liver shunts in dogs elucidate pathways regulating embryonic development and clinical disorders of the portal vein, Frank G. van Steenbeek et al., Mamm Genome. 2012 Feb; 23(1-2): 76–84.

[11] Aberrant gene expression in dogs with portosystemic shunts, Frank G. van Steenbeek et al., Plos One, 25 February 2013.

[12] The inheritance of extra-hepatic portosystemic shunts and elevated bile acid concentrations in Maltese dogs, C. A. O'Leary et al., Journal of Small Animal Practice, 55: 14–21, January 2014.