Portosystemic shunts: more common and more confusing than most realize (Proceedings)
Congenital portosystemic shunts (PSS) are much more common and certainly much more confusing than we ever imagined. At Texas A&M, we infrequently see the "classic" congenital PSS with the relatively straight forward presentation (i.e., young Yorkie with post prandial hepatic encephalopathy), probably because those cases are efficiently filtered out and never referred to us. Some breeds are more commonly affected (i.e., Yorkshire terriers, Pugs, Maltese, Schnauzers, Poodles, Shih Tzus, Havanese, Irish Wolfhound, Golden Retrievers, and Labrador Retrievers), but any dog may have a congenital PSS. We infrequently see classic post-prandial hepatic encephalopathy; rather, we more commonly see a young dog (e.g., one of the above breeds that is less than a year old) that is a "poor doer" who is not as big or as strong as the litter mates with very intermittent vomiting (i.e., "he or she has always had a sensitive stomach") and subtle signs of encephalopathy. Therefore, it is important to eliminate intestinal parasites and hypoglycemia in animals with suspected congenital PSS since the signs may be very similar. Polyuria-polydipsia can be a major clinical sign. In fact, in our practice, most young animals referred for possible central diabetes insipidus turn out to have hepatic disease, especially congenital PSS.
Classic hepatic encephalopathy consists of post-prandial seizures, coma, somnolence, blindness, head pressing and/or aggression. However, we are seeing more and more animals in which hepatic encephalopathy is manifested simply by their laying around a lot, acting tired or lethargic, or just not being interested in anything. In many cases, there is no obvious relationship between eating the signs. In some cases, about all you can say is that he patient has always been a "calm" dog and never really caused a lot of trouble by getting into things. In older dogs, the only comment by the owner may be that they dog is "getting older and slowing down a bit". To make matters more confusing, we are finding dogs that have hepatic encephalopathy that do not respond to medical management with lactulose or metronidazole. Some of these patients only quit having signs of hepatic encephalopathy when the shunt is surgically corrected. Therefore, you cannot allow lack of response to medical therapy help you decide whether or not a dog has hepatic encephalopathy due to a congenital PSS. Cats with hepatic encephalopathy due to congenital portosystemic shunting often have drooling as a major presenting complaint.
We sometimes see hematuria due to ammonium urate urolithiasis, but this usually often happens in older dogs (especially Schnauzers) that have had chronic hyperammonemia. Many times, this is the only clinical sign in the affected patient.Contrary to what is often described in textbooks, you can sometimes see major increases in ALT and SAP. We occasionally see patients with major increases in ALT (i.e., > 1,000 U/L) that appear to have acquired hepatic disease, probably toxic in nature. The ALT waxes and wanes with clinical signs. Our guess is that these dogs only have signs when they develop liver disease secondary to exposure to "toxins" that the atrophied liver cannot process because it is insufficient.
To further complicate the situation, we are seeing more and more dogs with congenital PSS that are being diagnosed for the first time when they are 7 or even > 10 years old. This appears to be especially common in Schnauzers, although other breeds may also be affected. Many times these patients have relatively minor signs that have been considered as normal for the particular patient (i.e., has always been a quiet dog, has always been a smallish dog, etc).
Ascites is exceedingly rare in animals with congenital portosystemic shunts. This is in distinction to dog with congenital hepatic AV fistula, which is another congenital vascular abnormality but which is entirely different from the standpoint of signs, diagnosis, and treatment. Ascites is relatively common in dogs with acquired portosystemic shunting. Therefore, if ascites is seen, one should first look for other hepatic diseases. In like manner, icterus is very seldom caused by congenital portosystemic shunts, and finding hyperbilirubinemia is an indication to first look for other diseases. In summary, congenital PSS present in a variety of ways, many of which are not the "classic" presentation that is described in textbooks.