Hepatic Microvascular Dysplasia in Dogs

What is hepatic microvascular dysplasia?

Hepatic microvascular dysplasia (sometimes called portal vein hypoplasia) is an inherited abnormality of the liver. In affected dogs, the microscopic blood vessels in the liver are underdeveloped or absent.

This reduces blood flow in the liver, causing the liver and its cells to atrophy (decrease in size). Due to this atrophy and decreased blood flow, the liver is less capable of processing toxins or producing proteins needed for growth and development.

Hepatic microvascular dysplasia is often found in dogs with other liver problems, such as a portosystemic shunt—a condition that prevents blood from being filtered by the liver. In some cases, hepatic microvascular dysplasia is the only liver problem present.

What causes hepatic microvascular dysplasia?

Hepatic microvascular dysplasia is a congenital defect, which means that animals are born with this condition. The condition is thought to have a genetic basis, although it is not fully understood. Yorkshire Terriers and Cairn Terriers are commonly affected by hepatic microvascular dysplasia. Other affected breeds include Miniature Dachshunds, Maltese, Miniature Poodles, Shih Tzus, Lhasa Apsos, Cocker Spaniels, Tibetan Spaniels, and West Highland White Terriers.

What are the signs of hepatic microvascular dysplasia?

The clinical signs of hepatic microvascular dysplasia vary significantly. Some dogs show no signs of liver disease, while others are severely affected. Most affected dogs show few clinical signs, and the disease may go undetected until adulthood. Clinical signs are more common and more severe in dogs that also have a portosystemic shunt or other liver abnormalities.

Growth and gastrointestinal signs: Puppies with hepatic microvascular dysplasia may show a “failure to thrive.” They may be abnormally small and slow to gain weight. As they get older, these dogs may demonstrate signs such as vomiting, diarrhea, or pica (eating non-food objects).

Urinary signs: Hepatic microvascular dysplasia can also cause urinary problems. Affected dogs may have increased thirst and urination, straining to urinate, or blood in the urine. Urinary stones may develop, and affected dogs may develop frequent urinary tract infections.

Neurological signs: Depending on the degree of liver dysfunction, some dogs may develop a condition known as hepatic encephalopathy (neurological dysfunction because of liver disease). Dogs with hepatic encephalopathy often show behavioral changes, such as head-pressing, abnormal vocalization, and ataxia (acting wobbly, as if drunk). They may also have seizures.

How is hepatic microvascular dysplasia diagnosed?

Your veterinarian may suspect hepatic microvascular dysplasia, or another liver disease, based on your dog’s medical history, physical examination, and laboratory test results. Affected dogs may have elevated liver values on blood tests, which can indicate liver disease. They may also be anemic (low red blood cell count) or have other bloodwork abnormalities. A urinalysis may show abnormally dilute urine, caused by increased thirst and urination associated with the disease.

If your veterinarian suspects liver disease, a pre- and post-meal serum bile acids test may be recommended. This test measures the concentration of bile acids in your dog’s blood before and after a high-protein meal. If the bile acids test is abnormal, the next step may be an abdominal ultrasound. 

Although hepatic microvascular dysplasia cannot be seen on ultrasound, it can help your veterinarian rule out a portosystemic shunt and other liver abnormalities. If no abnormalities are seen on ultrasound, your veterinarian will likely recommend a liver biopsy to assess for hepatic microvascular dysplasia. This biopsy may be performed during the ultrasound, using the ultrasound to guide an instrument into the abdomen to obtain a sample.

In some cases, your veterinarian may instead recommend a surgical biopsy of the liver. Regardless of how the sample is obtained, a biopsy is the only way to definitively diagnose hepatic microvascular dysplasia.

How is hepatic microvascular dysplasia treated?

Hepatic microvascular dysplasia is managed, not cured. There is no surgical or medical cure for the disease, so treatment focuses on controlling the symptoms. Dogs with no symptoms (asymptomatic disease) do not require treatment.

In dogs with hepatic encephalopathy, treatment typically relies on two major components that, together, can often minimize the signs of this condition.

• The protein content of the diet is decreased. This reduces the production of substances formed when protein is broken down, which contribute to the signs of hepatic encephalopathy. 
• Antibiotics (e.g., metronidazole, amoxicillin, or neomycin) or other medications (e.g., lactulose) are used to change the types of bacteria living in the intestines and further decrease the production of certain protein byproducts. 

Liver-supportive supplements (also called hepatoprotectants) are also frequently used to help manage hepatic microvascular dysplasia. Examples of commonly used hepatoprotectants include S-adenosylmethionine (SAMe), vitamin E, milk thistle, and ursodeoxycholic acid (ursodiol). These supplements are thought to decrease ongoing liver damage and help maintain healthy, functioning liver tissue.

Dogs with hepatic microvascular dysplasia should not be bred, due to the suspected inherited nature of this disorder.