Karen M. Tobias,     Knoxville, Tennessee

Signalment, History, and Clinical Signs

CPSS usually are diagnosed in immature animals, although a few animals are diagnosed at 10 years of age or older. Breeds most commonly affected with extrahepatic CPSS are Yorkshire terriers, Havanese, Maltese, Dandie Dinmont terriers, pugs, and miniature schnauzers. Intrahepatic CPSS are found primarily in large-breed dogs such as Irish wolfhounds and in medium-sized breeds such as Australian shepherds and Australian cattle dogs.

General clinical signs of CPSS include small stature, weight loss or failure to gain weight, polydipsia, and anesthetic or tranquilizer intolerance. Neurologic dysfunction from hepatic encephalopathy (HE) is seen in most animals with CPSS and may include lethargy, restlessness or pacing, ataxia, head pressing, circling, seizures, behavioral changes, and amaurotic blindness. Precipitating factors of severe neurologic signs (HE) include protein overload, hypokalemia, alkalosis, hypovolemia, hypoxia, gastrointestinal hemorrhage, infection, azotemia, constipation, drugs, and transfusion of stored red cells. Gastrointestinal clinical abnormalities may include anorexia, vomiting, diarrhea, or pica and, in large-breed dogs, evidence of gastrointestinal bleeding such as melena or hematemesis. Some dogs have no apparent signs or signs of only lower urinary tract disease or urinary tract obstruction. Many cats have hypersalivation and seizures, and some have unusual copper-colored irises.

Diagnosis

Differential Diagnoses

Single congenital portosystemic shunts must be differentiated from neurologic conditions such as hydrocephalus and epilepsy and from other primary hepatic diseases, including congenital PVH-MVD and multiple acquired shunts secondary to portal hypertension. Differentiation usually is based on results of advanced imaging; however, history, clinical signs, and results of blood work also may be helpful. Conditions other than CPSS should be suspected when neurologic or other clinical signs do not resolve with medical management of the HE.

Unlike animals with CPSS, ascites is a common finding on physical examination or ultrasonography in dogs with portal hypertension secondary to severe hepatocellular disease or hepatic arteriovenous malformations. With development of multiple acquired PSS, these animals have increased shunt fractions on scintigraphy.

Congenital portal vein hypoplasia is found in many small breeds predisposed to CPSS. Although results of liver biopsy are the same for both conditions, laboratory changes are usually less severe in dogs with PVH-MVD, unless noncirrhotic portal hypertension is present (see Chapter 146). Dogs with PVH-MVD are more likely to have normal red cell size (MCV); glucose, albumin, total protein, and cholesterol concentrations; and urine specific gravity and fewer if any at all clinical signs than dogs with CPSS. In addition, 90% to 95% of dogs with PVH-MVD have normal protein C activity and 81% have postprandial bile acids less than 75 µmol/L at the author’s institute. Results of scintigraphy, portography, and CT angiography are usually normal in dogs with PVH-MVD.