Hepatic Microvascular Dysplasia
What is hepatic microvascular dysplasia?
Hepatic microvascular dysplasia is an inherited abnormality of the liver. In affected dogs, the microscopic blood vessels within the liver are underdeveloped or absent. This decreases blood flow within the liver, causing atrophy (a decrease in size) of the liver and its cells. Due to this atrophy and decreased blood flow, the liver is less capable of processing toxins and producing proteins that are needed for growth and development.
Hepatic microvascular dysplasia is often found in dogs that have other liver problems, such as portosystemic shunts. In some cases, however, microvascular dysplasia can exist as an isolated abnormality.
What causes hepatic microvascular dysplasia?
"The condition is thought to have a genetic basis, although this is not fully understood."
Hepatic microvascular dysplasia is a congenital defect, meaning that animals are born with this condition. The condition is thought to have a genetic basis, although this is not fully understood.
The breeds most commonly affected with hepatic microvascular dysplasia are Yorkshire Terriers and Cairn Terriers. Other commonly-affected breeds include Miniature Dachshunds, Maltese, Miniature Poodles, Shih Tzus, Lhasa Apsos, Cocker Spaniels, and West Highland White Terriers.
What are the clinical signs of hepatic microvascular dysplasia?
The clinical signs of microvascular dysplasia vary significantly, with some dogs showing no clinical signs of liver disease and others being severely affected. Most affected dogs show few clinical signs and microvascular dysplasia may go undetected until adulthood. Clinical signs are more common, and more severe, in dogs who also have a portosystemic shunt or other liver abnormality.
Dogs with microvascular dysplasia may show what is referred to as a “failure to thrive.” As puppies, affected dogs may be abnormally small and slow to gain weight as puppies. As they get older, these dogs may demonstrate signs such as vomiting, diarrhea, or pica (eating non-food objects).
Depending on the degree of liver dysfunction, some dogs may develop a condition known as hepatic encephalopathy. Hepatic encephalopathy occurs when toxins build up in the blood stream, affecting the brain. Dogs with hepatic encephalopathy often have behavior changes, such as head pressing, abnormal vocalization, ataxia (acting wobbly, as if drunk). They may also have seizures. These signs often are seen to be most severe after ingestion of a high-protein meal.
Microvascular dysplasia can also cause urinary difficulties. Affected dogs may exhibit increased thirst and urination, straining to urinate, or blood in the urine. Urinary stones may develop, and/or affected dogs may develop frequent urinary tract infections.
How is hepatic microvascular dysplasia diagnosed?
Your veterinarian may suspect microvascular dysplasia or other liver disease based on your dog’s history, physical examination findings, and screening laboratory results. On screening labwork, affected dogs may have elevated liver values. They may also be anemic (low red blood cell count) or have other bloodwork abnormalities. Urinalysis (examination of your dog’s urine) may show abnormally dilute urine, caused by the increased thirst and urination that may be seen with microvascular dysplasia.
In many cases, a veterinarian who suspects liver disease will perform a pre- and post-meal serum bile acids test. In this test, your veterinarian will measure the concentration of bile acids in your dog’s blood before and after a high protein meal. Bile acids levels may be elevated in dogs with liver disease before and/or after a meal; examining these values may help to increase the suspicion of microvascular dysplasia or other liver disease.
If the bile acids test is abnormal, the next step may be an abdominal ultrasound. Although microvascular dysplasia cannot be seen on ultrasound, an ultrasound allows your veterinarian to rule out a portosystemic shunt and other liver abnormalities. If no other abnormalities are seen on ultrasound, your veterinarian will likely recommend a biopsy of the liver to assess for the presence of microvascular dysplasia. This biopsy may be performed at the same time as the ultrasound, using the ultrasound to guide an instrument into the abdomen to obtain a biopsy 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 microvascular dysplasia.
How is hepatic microvascular dysplasia treated?
"Microvascular dysplasia is a condition that is managed, not cured."
Microvascular dysplasia is a condition that is managed, not cured. There is no surgical or medical cure for microvascular dysplasia; therefore, therapy is directed at controlling the clinical signs of this condition.
Dogs with asymptomatic microvascular dysplasia do not require any treatment.
In dogs with hepatic encephalopathy, treatment typically relies on two major components. First, the protein content of the diet is decreased. This results in the production of decreased quantities of protein breakdown products that contribute to the signs of hepatic encephalopathy. Secondly, antibiotics (such as metronidazole, amoxicillin, or neomycin) or other medications (such as lactulose) are frequently used to alter the bacterial population within the intestines and further decrease production of certain protein metabolites. With these measures, the signs of hepatic encephalopathy can often be minimized.
Hepatoprotective supplements (supplements intended to help protect the liver) are also used frequently in the management of microvascular dysplasia. Examples of commonly used hepatoprotectants include S-adenosylmethionine (SAMe), vitamin E, Milk Thistle, and Ursodeoxycholic acid. These supplements are thought to decrease ongoing liver damage and help keep the remaining, functioning liver tissue healthy.
Dogs with microvascular dysplasia should not be bred, due to the suspected genetic component of this disorder.
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