Portosystemic Shunts (PSS)

This is an uncommon condition affecting the liver of a dog and can be life-threatening. In most cases, the problem occurs during development of the puppy. There is a large vein called the portal vein, which connects the gastrointestinal system to the liver, where it carries toxins and by-products to the liver to be processed and removed from the body. When the puppy is in the womb, this vein is closed off so that nutrient-rich blood from the mother can go directly via an extra blood vessel (called the ductus venosus) to the puppy’s vital organs (heart and brain), without needing to be processed by the liver first. Usually when the puppy is born, the extra vessel closes off and the portal vein opens. In liver shunt cases, the portal vein remains closed and the extra vessel is still present, meaning that the liver is essentially “by-passed”, so toxins and by-products remain in the bloodstream instead, causing the dog to become ill.

As the puppy grows up, the following clinical signs may be noticed:

- stunted growth

- poor muscle development

- weight loss

- neurological behaviours, eg disorientation, staring into space, head pressing, circling

- seizures

- drinking and urinating a lot

- vomiting and diarrhoea

Most cases are diagnosed at 1 year old but some cases can be seen much earlier or much later in life.

Some breeds are predisposed to this condition including; Yorkshire Terriers, Old English Sheepdogs, Irish Wolfhounds, Cairn Terriers and Beagles.

Diagnosis is based on clinical signs and diagnostic tests. These usually include blood tests to assess liver function and abdominal imaging, such as ultrasound or CT scans.

The treatment options are medical or surgical.

Medical management involves use of a special low protein diet, lactulose and antibiotics to help to reduce the amount of toxins that are produced and absorbed in the large intestines. This then reduces the amount of toxins that are getting into the bloodstream. About a third of cases managed this way live a relatively long life. However, for dogs with more severe clinical signs, such as uncontrollable seizures, medical management is often not enough.

Surgery in these cases is usually performed by a soft tissue specialist as the technique is complicated and advanced. Under general anaesthesia, the extra blood vessel is located and a device is placed around it to slowly close it over the next 3-4 weeks. The vessel needs to close over time so that the liver is not overwhelmed. The surgery is complicated because the extra vessel could be located on the outside of the liver but it could also be located on the inside of the liver, making it more challenging to place the device. In most cases, surgery provides the best chance for a long life, many dogs having no clinical signs 4-8 weeks after surgery. Medical management is continued for several weeks after surgery but some dogs need to continue on medical management post-surgery for life.

With thanks to Dr Elizabeth Mollard MRCVS, small animal vet and Schnauzerfest volunteer