Lifespan and Causes of Death in the Irish Wolfhound - Vetsuisse ...

3.2 Intrahepatic Portosystemic Shunt (PSS)
3.2.1 Description
Portosystemic Shunt in Wolfhounds is a congenital malformation of the porto-caval
blood vessels, leading to gastro-intestinal and neurological symptoms. The condition
is hereditary (simple autosomal recessive; see 3.2.3), but the exact mechanism that
causes the Ductus venosus to remain open is not known (Meyer, Rothuizen et al.
1995; White, Burton et al. 1998; Ubbink, van de Broek et al. 1998 b; Hunt 2004).
3.2.1.1 Pathophysiology
In healthy dogs, blood rich in nutriments and ammonia coming from the intestine
passes through the portal vein to the liver, where it passes through a capillary system
and its many components are chemically modified and detoxified before being
released into the main circulatory system. In the foetus, this mechanism is not
necessary, and the capillary system of the liver is therefore bypassed by the Ductus
venosus, which closes soon after birth in healthy dogs (Broome, Walsh et al. 2004).
In Irish Wolfhounds affected with PSS, this vessel fails to occlude after birth, which
causes a leaking of toxic metabolic products into the bloodstream, leading to the
typical symptoms of hepatic encephalopathy. Anatomically, the persistent Ductus
venosus is located intrahepatically in the left liver division (White, Burton et al. 1998).
3.2.1.2 Symptoms
Patients with PSS often exhibit non-specific symptoms such as stunted growth,
intermittent anorexia, depression, vomiting, PU/PD and behavioural changes. Signs
of hepatic encephalopathy (ataxia, stupor, head pressing, seizures etc.) are often
intermittent and usually worsen after feeding, especially when a high protein diet is
used (Watson and Herrtage 1998; Fossum and Hedlund 2002). Affected dogs
typically develop symptoms before one year of age (Broome, Walsh et al. 2004).
3.2.1.3 Diagnosis
Most affected animals are microhepatic on X-rays (Fossum and Hedlund 2002), and
it is usually possible to demonstrate an intrahepatic PSS through ultrasonography
(Suter and Niemand 2001 a). Scintigraphy following rectal administration of TcO 4 is
another possible way of diagnosis – in case of a shunt, the marker reaches the heart
before or at the same time it reaches the liver (Bernhardt, Westhoff et al. 1996).
Haematological signs may include normochromic microcytosis, mild nonregenerative
anaemia, target cell formation or poikilocytosis. Plasma albumin and BUN may be
lowered due to reduced liver function. ALAT, ASAT and AP may be slightly raised,
while serum bilirubin is usually normal (Fossum and Hedlund 2002). Urate crystals
may be found in the urine of up to 50% of affected dogs (Suter and Niemand 2001 a).
Wolfhound puppies can be screened for the presence of a PSS from about six weeks
of age through measuring postprandial serum bile acid levels between 90 to 120
minutes after feeding. A deliberately low threshold value of 30 μmol per litre is set in
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