Signalment

Intrahepatic CPSS are more common in large breed dogs with an increased prevalence in Irish Wolfhounds, Labrador Retrievers, Golden Retrievers, Australian Shepherds, Australian Cattle Dogs, German Shepherd Dogs, Doberman pinschers, Irish Setters, and Samoyeds.^3,4 Extrahepatic CPSS are more common in small and toy breed dogs including Havanese, Yorkshire Terrier, miniature schnauzer, pug, Shih tzu, Bichon fries, Jack Russell Terrier and maltese.^3,4 Extrahepatic CPSS are more common in cats with increased prevalence in DSH, Siamese, Himalayan, Persian, and Burmese.^3,5 There is evidence of a genetic predisposition in Yorkshire terriers, Cairn terriers, maltese, Irish Wolfhounds, and Australian Cattle Dogs but the mode of inheritance is unknown.^3,6,7,8 Cairn terriers and Yorkshire Terriers also have an increased incidence of PHPV.⁴ In dogs and cats with CPSS, congenital arterioportal fistulas and PHPV, signs are most commonly seen in young animals but occasionally older animals are diagnosed.^3,4 In general, animals with less severe forms of PHPV present with milder signs at an older age than those with CPSS.³ Dogs with acquired portosystemic shunts may be young if they form secondary to congenital arterioportal fistulas or PHPV. Animals with acquired portosystemic shunts may be older if the collaterals have formed secondary to extensive fibrosis or cirrhosis.

Clinical Findings

The severity of signs depends on the size of the shunt (bigger is bad) and type of shunt.³ For example, a splenocaval shunt does not contain blood from the gi tract and less portal blood is diverted so signs may be slower in onset and milder than with an intrahepatic shunt in which a large volume of portal blood is diverted. As discussed above, less severe forms of PHPV may present with more mild signs than CPSS.³

Laboratory Findings

There may be no laboratory abnormalities. A microcytic normocytic normochromic anemia may be seen with CPSS and is believed to be due to iron deficiency.⁹ Microcytosis is not seen with PHPV. Abnormalities in erythrocyte shape and target cells may be observed and due to cholesterol abnormalities.³ Decreases in albumin, cholesterol, blood urea nitrogen, and glucose are relatively common in animals with CPSS.³ Liver enzymes may be normal or mildly increased.³ Urine is often isosthenuric or hyposthenuric and increased protein as well as ammonium urate crystals may be seen.⁴ Clotting function (PT, aPPT, clotting factors, platelets) is abnormal in dogs with CPSS.^10,11 Spontaneous hemorrhage is not usually a problem with these animals but intra-operative hemorrhage can be severe.

Serum bile acids have historically been the most common test utilized to screen for portosystemic shunting. It is important to obtain both fasting and post-prandial samples. Spot urine bile acids can also be performed with a similar sensitivity and specificity to serum bile acids for diagnosing liver disease in dogs.¹² The advantage of urine testing is that no venipuncture is required. Resting blood ammonia is a fairly sensitive test for hepatic disease in animals displaying hepatic encephalopathy but an ammonia challenge (oral, rectal) may be required for asymptomatic animals or with a prolonged fast. Ammonia tolerance testing should never be performed on animals with hepatic encephalopathy as it may worsen their signs. Neither bile acids or ammonia levels can differentiate between types of liver disease. There is evidence that fasting blood ammonia is a more sensitive and specific indicator of portosystemic shunting than fasting bile acids but obtaining a post-prandial bile acid increases the sensitivity of bile acids dramatically for diagnosing portosystemic vascular anomalies.^13,14