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Portosystemic Shunt in Dogs (Symptoms, Causes & Treatment)

A portosystemic shunt is a lesser-known condition that, despite its relative obscurity, can have profound implications for your canine companion. As pet parents, we all want the best for our dogs, and knowledge is power. Awareness of this condition can aid in early detection and make a significant difference in your furry friend's outcome. 

Portosystemic shunting in dogs, also known as a liver shunt, is a condition in which the blood bypasses the liver. But how dangerous is it? Keep reading to learn more about portosystemic shunt in dogs to understand its causes, symptoms, and treatment options available. 

What is a Portosystemic Shunt?

A portosystemic shunt (PSS) is a vascular anomaly in dogs where blood bypasses the liver, either partially or completely. Also known as a liver shunt, this condition means that the liver is deprived of the blood flow it needs to receive nutrients, oxygen, and growth factors, and the liver can't filter out toxins from the bloodstream properly. [1] 

In a normal circulatory pattern, blood from the intestines, stomach, pancreas, and spleen is filtered through the liver via the portal vein. The liver detoxifies the blood, removing waste products, drugs, and other toxins before the blood returns to the general circulation through the heart. [1] 

When a dog has a portosystemic shunt, the blood bypasses the liver, and these waste products and toxins can build up in the bloodstream, leading to a range of health problems. 

Two main types of canine portosystemic shunts

There are two main types of canine portosystemic shunts: 

  • Congenital: The dog is born with the shunt, usually due to a genetic defect. Breeds most commonly affected include Miniature Schnauzers, Yorkshire Terriers, Cairn Terriers, Maltese, Australian Cattle Dogs, Golden Retrievers, Old English Sheepdogs, and Labrador Retrievers. [1]
  • Acquired: These develop later in life due to liver disease or other conditions that increase resistance to blood flow within the liver. [1]

Detecting and treating portosystemic shunts in dogs as early as possible is essential because prolonged exposure to toxins not filtered by the liver can lead to serious health complications.

Symptoms of Portosystemic Shunts in Dogs

Dogs with portosystemic shunts often exhibit a range of clinical signs, with symptoms varying depending on the severity of the shunt and the amount of blood bypassing the liver. 

Symptoms of portosystemic shunts in dogs

Some of the most common symptoms of portosystemic shunts in dogs include the following: 

  • Stunted growth: Dogs with congenital portosystemic shunts often grow slower than others and are smaller. [2] 
  • Neurological abnormalities: A buildup of toxins in the blood can lead to encephalopathy, which affects brain function. Signs can include head pressing, disorientation, seizures , and coma in extreme cases. [2] 
  • Gastrointestinal issues: Affected dogs can have recurrent gastrointestinal problems like diarrhea , vomiting, decreased appetite, and weight loss. [1] 
  • Increased drinking and urination: Known as polydipsia and polyuria, these symptoms can be due to the body's attempt to rid itself of accumulated toxins. Other urinary issues include difficulty urinating and blood in the urine. [2] 
  • Lethargy: Dogs with portosystemic shunts may seem unusually tired, displaying reduced energy or enthusiasm for activities they once enjoyed. 
  • Ptyalism: Also known as excessive drooling, dogs may experience ptyalism due to GI issues associated with portosystemic shunting or due to hepatic encephalopathy, a nervous system disorder caused by severe liver damage. [1]

The symptoms of canine portosystemic shunts can be intermittent, and some dogs may appear normal between episodes. Also, not all dogs with portosystemic shunt will show all these symptoms, and the clinical presentation can vary widely. If your dog is experiencing PSS symptoms, consult a vet as soon as possible. Early intervention can significantly improve the prognosis for these dogs. 

What Causes Portosystemic Shunts in Dogs?

Portosystemic shunting can either be present at birth or developed later in life. Congenital PSS is the most common form in dogs, arising due to the abnormal development of the fetal blood vessels in the liver before birth. Congenital portosystemic shunts in dogs are more commonly observed in certain breeds like small dogs. However, it can also be seen in large breeds. [1]

List of breeds that are predisposed to portosystemic shunts

Conversely, acquired portosystemic shunts in dogs are developed late in a dog's life due to conditions that increase the resistance to blood flow within the liver. This resistance forces the blood to find alternative pathways, bypassing the liver. [1] Common causes of acquired PSS include: 

  • Chronic liver diseases: Liver diseases in dogs encompass a range of conditions that can cause prolonged damage to the liver. Examples include hepatitis, liver tumors, fibrosis, portal vein thrombosis, and more. 
  • Cirrhosis: Scarring of the liver tissue, often due to chronic liver diseases. 
  • Portal vein hypertension: Increased blood pressure in the portal vein can create new, abnormal blood vessel connections. [3]

Diagnosing & Treating Portosystemic Shunts in Dogs

The first step to diagnosing portosystemic shunts in dogs is a clinical examination, where the vet will take note of any signs and symptoms that may suggest a liver issue. They'll also perform diagnostic testing, such as: 

  • Blood tests: These can reveal elevated liver enzymes, low blood urea nitrogen, or changes in the bile acids. A bile acid test is particularly important for assessing the liver's ability to process bile. Elevated bile acid levels are a strong indicator of PSS in dogs.
  • Imaging: Imaging tests like ultrasound, radiograph (x-rays), and portography can reveal more information for the vet to make a definitive diagnosis. Ultrasound can detect abnormal blood vessels and give a visual assessment of the size of the liver and blood flow, while X-rays can provide information on the liver's size and rule out other conditions. Portography is a specialized X-ray using a dye in the portal vein to visualize the blood flow and detect the shunt. [1]

Once your vet has diagnosed your dog with a portosystemic shunt, they'll devise a treatment plan. Surgical ligation is the most definitive treatment for PSS. The abnormal vessel is tied off during this procedure, forcing blood to flow through the liver. The process can be done in stages if the shunt is large to prevent a sudden increase in portal blood pressure. [1] 

Unfortunately, not all dogs are suitable candidates for surgery, especially if they have multiple shunts or another underlying health issue. Medical management is focused on reducing the symptoms and complications associated with the shunt to prepare the dog for surgery with fewer complications. [1] Typically, this treatment consists of dietary changes, medication, antibiotics, and supplements to support liver function and reduce the amount of ammonia and other toxins in the liver. [1]

FAQs

What is the life expectancy of a dog with a portosystemic shunt?

Portosystemic shunts in dogs can lead to a variety of health issues if left untreated. However, the life expectancy of a dog with this condition depends on several factors, including the type of shunt, timeliness of diagnosis and treatment, treatment type, and severity of the symptoms. 

In general, dogs diagnosed and treated early often have a better prognosis. Untreated shunts can lead to liver issues, neurological problems, and other systemic complications due to the buildup of toxins in the bloodstream that are normally removed by a healthy liver. 

Surgical ligation is the preferred method for shunts. When successful, surgery can significantly prolong a dog's life and improve its quality of life. Post-surgical complications can arise, but many dogs live a normal lifespan following successful surgery. Conversely, medical management doesn't correct the shunt, so a dog's lifespan might be reduced compared to surgically treated dogs. However, many can live for several years with appropriate management.

In a study comparing medical and surgical treatments for dogs with congenital portosystemic shunt, dogs that underwent surgery had a notably higher survival rate compared to those treated medically. The surgical group also exhibited fewer clinical signs over all the tracking intervals, with a significant difference observed 4 to 7 years after the study ended. [4]

Can portosystemic shunts be managed?

Portosystemic shunts can be managed, but the treatment often depends on the symptoms. For instance, dogs showing neurologic signs may require intravenous fluids, while seizures may be treated with diazepam or other benzodiazepines. [5]

Management may also include a protein-restricted, digestible diet. Prescription diets are often recommended while supplementing them with antibiotics and addressing GI issues to help manage symptoms. [5]

The best management is treatment. Again, surgery is optimal for single congenital shunts to promote blood flow return and tissue regeneration. Experienced surgeons usually handle these cases rather than your general vet. [5]

What does a portosystemic shunt look like?

To visualize a portosystemic shunt, you would need to use medical imaging. On an ultrasound, the shunt can look like an abnormal blood vessel connection that isn't seen in normal anatomy. 

Depending on the type and location of the shunt, its appearance can vary. However, without medical training, it might be difficult for you to identify PSS by just looking at imaging results. 

A trained veterinarian or veterinary radiologist would typically make the diagnosis. However, pet parents might see visual symptoms in dogs suffering from portosystemic shunts. These symptoms can range from subtle to severe, depending on the extent of the shunt and the dog's overall health. Common symptoms include:

  • Stunted growth
  • Neurological abnormalities and strange behavior
  • Gastrointestinal issues
  • Increased thirst and urination
  • Lethargy
  • Weight loss
  • Recurrent fever

Keep in mind that while these symptoms can indicate portosystemic shunt, they can also be seen with other diseases and conditions. If you suspect your dog is suffering from PSS or any other health issue, you should seek veterinary attention as soon as possible. 

Close-up of dog laying in dog bed looking up with tongue out

Final Notes 

Portosystemic shunts in dogs are a significant medical concern that can lead to a range of physical symptoms, from GI issues to neurological abnormalities. By allowing blood to bypass the liver, toxins build up in the bloodstream, leading to various health issues. Early detection and intervention are crucial for improving your dog's quality of life. 

To ensure the best for your dog, always keep an eye out for any unusual behavior or symptoms and talk to a vet as soon as you notice any issues. For a more convenient approach, try Dutch. With telemedicine for pets, you can get professional advice without the stress of a veterinary clinic visit. Offering easy access to licensed veterinarians, we ensure your pet receives high-quality care in just a few clicks.

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References

  1. "Portosystemic Shunts." American College of Veterinary Surgeons, 20 June 2023, www.acvs.org/small-animal/portosystemic-shunts/. 

  2. "Portosystemic Shunt." ScienceDirect Topics, www.sciencedirect.com/topics/veterinary-science-and-veterinary-medicine/portosystemic-shunt. 

  3. Center, Sharon A. "Acquired Portosystemic Shunts in Small Animals - Digestive System." Merck Veterinary Manual, 5 Oct. 2023, www.merckvetmanual.com/digestive-system/hepatic-diseases-of-small-animals/acquired-portosystemic-shunts-in-small-animals. 

  4. Greenhalgh, Stephen N et al. "Long-term survival and quality of life in dogs with clinical signs associated with a congenital portosystemic shunt after surgical or medical treatment." Journal of the American Veterinary Medical Association vol. 245,5 (2014): 527-33. doi:10.2460/javma.245.5.527

  5. Tobias, Karen M M. "Tobias Portosystemic Shunts" University of Illinois College of Veterinary Medicine, vetmed.illinois.edu/wp-content/uploads/2015/09/54.-Portosystemic-Shunts.pdf

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