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Genetic Liver Abnormality in Dogs

Hepatoportal Microvascular Dysplasia in Dogs

Hepatoportal microvascular dysplasia (MVD) is a liver condition characterized by abnormal blood vessels within the liver, leading to the bypass of blood between the portal vein and the systemic circulation. This abnormality can result from microscopic lesions, abnormal development, positioning issues, or constriction caused by excessive smooth muscle, impeding proper blood flow. The condition affects various liver lobes to varying degrees, with some severely affected and others minimally so. Manifestations of MVD typically arise when bile fails to perform its normal functions due to the impaired blood flow to the liver.

Primarily observed in certain small dog breeds, MVD has a genetic basis with strong evidence of inheritance in breeds such as Yorkshire terriers, Maltese dogs, Cairn terriers, Tibetan spaniels, Shih Tzus, Havanese, and others. While symptoms may not always be present (asymptomatic), when they do occur, they often manifest as nonspecific gastrointestinal issues like vomiting, diarrhea, and loss of appetite.

The inheritance of MVD is not dependent on gender or geographical location and has a global distribution. It may be governed by a dominant gene that does not affect all individuals, as unaffected parents can produce affected offspring. Alternatively, it could be influenced by multiple genes. Diagnosis typically involves a total serum bile acids (TSBA) test, which serves as a marker for the condition. In certain small dog breeds, the prevalence of MVD ranges from 30 to 70 percent, while it is rare to non-existent in large dog breeds. Typically, MVD is detected in asymptomatic juveniles by four to six months of age, with some cases identified as early as six weeks.

Symptoms

Symptoms of hepatoportal microvascular dysplasia (MVD) in dogs typically manifest as gastrointestinal issues, dividing affected dogs into two groups: asymptomatic and symptomatic. However, it’s more probable for dogs with the anomaly to display symptoms. Gastrointestinal complications such as vomiting, anorexia (lack of appetite), diarrhea, and lethargy are common indicators of MVD.

Asymptomatic dogs are often diagnosed during routine screenings or diagnostic assessments for other health concerns, especially within families known to have a prevalence of the disorder. Diagnosis of this congenital inherited disorder relies on total serum bile acids (TSBA) testing before clinical signs attributable to MVD appear; however, concurrent illnesses may complicate interpretation. Unlike dogs with other liver conditions, those with MVD rarely develop abdominal fluid accumulation. Typically, asymptomatic dogs have an uneventful medical history; occasionally, they might exhibit delayed recovery after anesthesia or sedation or demonstrate drug intolerance.

Causes

Inherited congenital disorder

Diagnosis

To diagnose this condition, it’s important to provide your veterinarian with a detailed history of your dog’s health, including any symptoms experienced and information about familial lines if available.

In asymptomatic young dogs, the condition is often identified through elevated total serum bile acids values or the presence of hepatic encephalopathy, which involves damage to the brain and nervous system as a complication of liver disorders. In symptomatic dogs older than two years, shunting typically occurs due to acute or chronic inflammatory, tumor, or toxic liver conditions.

The microscopic characteristics of several disorders causing hepatic portal fluid deficiency resemble those of hepatoportal microvascular dysplasia. Your veterinarian may conduct a liver biopsy to examine liver tissue microscopically, perform aspiration needle biopsies to analyze fluid, and obtain wedge or laparoscopically retrieved liver samples for further evaluation.

Treatment

For asymptomatic dogs, there is no specific medical intervention recommended. However, it’s crucial to monitor for any adverse reactions to medications and avoid prescribing selected drugs or implementing dietary protein restrictions without consulting your veterinarian first.

Dogs experiencing brain and nervous system damage as a complication of liver disorders or prolonged vomiting or diarrhea may require hospitalization for supportive care and diagnostic assessments. These dogs likely have additional disorders or a complicated form of MVD. Mild cases of brain and nervous system damage stemming from liver disorders can be managed with a veterinarian-approved protein-restricted diet and appropriate medical treatment.

Prevention

Currently, there are no recommendations for completely eliminating MVD from a specific genetic line or breed. Despite efforts based on extensive pedigrees of Yorkshire terriers, Cairn terriers, Tibetan spaniels, Maltese, Shih Tzus, and Havanese dogs, breeding unaffected parents does not guarantee the elimination of MVD within a family lineage. The genetic defect involves vascular malformations, predominantly affecting the liver but potentially extending beyond this organ. In families with a high incidence of MVD, it’s essential to remain vigilant for dogs exhibiting vague signs of illness that may indicate a portosystemic vascular anomaly. Surgical exploration and some standard tests may overlook this condition.

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