Disease Ontology ID: DDTO:0000990

Disease Description: Portosystemic shunt (PSS) is a birth defect of the circulation in the liver.

Inherit Mode: The exact mode of inheritance is not known, but a genetic basis is clearly indicated by higher-than-average occurrence in certain breeds (see below).

Disease Symptom: The symptoms of PSS tend to emerge during puppyhood. These symptoms generally are associated with the central nervous system, the gastrointestinal tract, or the urinary tract. Most consistently, there are signs of hepatic encephalopathy - neurological and behavioural evidence of diffuse brain dysfunction due to liver dysfunction. Examples include loss of appetite, mental dullness, lethargy and sluggishness, weakness, poor balance, disorientation, blindness, seizures, and even coma. The symptoms may wax and wane, and may worsen after eating a protein-rich meal. With PSS, a pup's growth may seem to be stunted or slower than the growth of littermates and age-mates. Indeed, "runts" of litters often turn out to be puppies that have birth defects, and PSS is a very common one of these. Failure of the liver to clear ammonia means that there will be increased excretion in the urine. This commonly leads to urolithiasis - kidney, bladder, or urethral calculi (stones) due to the build-up of mineral salts. Any young dog with urolithiasis (stones in the bladder, urethra, or kidneys) should be checked for PSS. The first sign of PSS in a dog may be a prolonged recovery from anesthesia, or excessive sedation after treatment with some medications. This occurs because with PSS, anesthetics and medications are not filtered out of the blood and broken down as they would normally be by the liver, but instead are recirculated in the body. The impact of PSS may not be apparent at first. Symptoms tend to worsen with age, and the decision to treat (via surgery) should be made as early as possible. Dogs do not outgrow PSS; surgery should be performed when a puppy is still growing, to minimize the risk of permanent damage. Dogs who are not candidates for surgery, either because they have a form of PSS that is inoperable or because surgery is not an option due to cost or availability, may still benefit from orally-administered medications at home. It is very important to realize that the final result of surgery for PSS can only be known weeks after the surgery has been done. The effects of PSS take time to subside, and the body's ability to adapt back to normal after the surgical correction is different in every dog: many become totally normal and have normal lives, whereas some have irreversible damage associated with the PSS, and surgery only partially corrects these changes.

Disease Cause: -

Disease Diagnose: Generally, the diagnosis of PSS is suspected based on a combination of the medical history (such as delayed anesthetic recovery or previous surgery for urolith/urinary tract stone removal), symptoms (such as those described above), and results of laboratory tests. The screening test of choice is a routine laboratory panel (complete blood count, serum biochemistry profile, and urinalysis) with serum bile acids, which is a specific blood test that requires a 12-hour fasting period beforehand and takes 2-3 hours. The confirmatory test of choice is a high-detail abdominal ultrasound examinationby a specialist (radiologist or internist); nuclear scintigraphy (atype of scan) also is highly definitive but is less widely available. Either test is noninvasive and is generally done without sedation. The screening blood test, serum bile acids, is highly accurate, with a nearly 100% ability to detect PSS in dogs that have it. A positive test still requires ultrasound/scan confirmation, because other disorders such as hepatic microvascular dysplasia, which is an incurable, microscopic version of PSS where thousands of small shunts ("shortcuts") cause blood to bypass the liver at the tissue level, may be present instead. Hepatic microvascular dysplasia can only be confirmed with a liver biopsy, so it is routine for dogs that undergo surgery for PSS to also have a liver biopsy, for identifying whether hepatic microvascular dysplasia is also present. This alters the long-term outlook: dogs with PSS but without microvascular dysplasia have a better long-term outlook for living free of symptoms and without medications.

Treat Method: The most definitive way to deal with PSS is surgery. The surgeon identifies the path of blood bypassing the liver and closes it, forcing the blood to follow the new, normal course through the liver. This type of surgery is an open-abdominal procedure, meaning general anesthesia is warranted and a period of recovery, typically lasting 1-4 days in the hospital and 2 weeks or so at home, is to be expected. The success rate of surgery is high (>90%) but not perfect; even in the most experienced hands, some dogs with PSS who also have microvascular dysplasia or other circulatory defect through the liver may not tolerate the operation and may need only partial closure of the shunt. Other dogs do not tolerate any correction of PSS and this is only apparent during the operation. To improve the chances of success, surgeons often repair PSS by inserting a device that closes the PSS gradually, over several weeks. Surgeons also will be careful to monitor a dog's status both before the surgery and during the post-operative period; the liver performs so many essential functions that careful monitoring and medical support, such as with plasma transfusions, antibiotics, or other treatments, are essential. In some cases, PSS may involve a single shunt that is buried deep within the liver tissue: intra-hepatic PSS. These situations are difficult to correct in the manner described above, and a better option in such cases is minimally-invasive occlusion (closure) of the shunt through catheter-based techniques. Briefly, this approach does not involve surgical opening of the abdomen but rather involves a surgeon placing a catheter through a blood vessel in the groin and steering the catheter to the location of the shunt within the liver under fluoroscopic, real-time X-ray guidance. The surgeon can then deploy a device that occludes (blocks) blood flow at that level, redirecting it into the normal path. This is an extremely challenging procedure performed only at certain specialist referral hospitals; discussing this possibility with a general practitioner veterinarians is the first step, followed by referral if the features of the PSS are compatible with this procedure. Finally, many dogs with very mild or no symptoms of PSS, especially if the condition is first identified after 5 years of age, may do well simply by receving oral medications and no surgery at all. To be clear, definitive (surgical) correction is the best treatment, but if the PSS is very minor and it escapes notice until age 5 years or thereafter, there may be more to be gained with a conservative approach and no surgery.

Breeder Advice: Affected individuals and their parents should not be used for breeding. Siblings should only be used after careful screening. If any affected offspring are born, breeding of the parents should be discontinued.

Disease Description Source: Link