Hepatoportal Microvascular Dysplasia (HMD)
Hepatoportal microvascular dysplasia (MVD) is a blood vessel abnormality inside the liver that causes shunting (bypass) between the portal vein (the blood vessel that connects the gastrointestinal tract with the liver) and circulation into the system. It may be caused by microscopic lesions on the liver, abnormal development, abnormal positioning, or throttling due to a prominent smooth muscle that prevents blood flow. The lobes of the liver are involved, some severely, others very little. This is suspected when the bile is not doing its work. In short, because of malformations in the blood vessels, the blood is not flowing to the liver as it should.
This is a rare disease of genetic origin in certain small-breed dogs. There is compelling evidence of inheritance in Yorkshire terriers, Maltese dogs, Cairn terriers, Tibetan spaniels, shih-tzus, Havanese, and others. It is rarely without symptoms (asymptomatic). The symptoms are usually vague gastrointestinal signs: vomiting, diarrhea, and lack of appetite.
Inheritance is not gender or regionally linked; it is found worldwide. It may be adominant gene that does not affect all members, since unaffected parents may produce affected offspring, or it may be caused by more than one gene. A total serum bile acids (TSBA) test is used as the marker for this condition. Prevalence in certain small-breed dogs ranges from 30 to 70 percent. It is rare to non-existent in large-breed dogs. It is usually detected in asymptomatic juveniles by four to six months of age, or as early as six weeks.
While two groups have been described (asymptomatic and symptomatic), it is most likely that dogs with the anomaly will be symptomatic. Symptoms are indicative of gastrointestinal complications: vomiting, lack of appetite (anorexia), diarrhea, andlethargy.
Asymptomatic dogs are typically diagnosed in the course of routine screening or diagnostic evaluations for unrelated health problems, or on routine testing in kindreds with a known prevalence of the disorder. Congenital inherited disorder is diagnosed by total serum bile action (TSBA) before clinical signs are attributed to a microvascular tumor (MVD); concurrent illnesses may complicate the interpretation. Dogs with a microvascular tumor rarely, if ever, develop an accumulation of fluid in the abdominal cavity. Asymptomatic dogs usually have an unremarkable history; occasionally, they will display a delayed recovery after anesthesia or sedation, or show drug intolerance.
Congenital inherited disorder
You will need to give your veterinarian a thorough history of your dog's health, including a background history of symptoms, if any, and any information you might have regarding familial lines.
This condition is attributed in any asymptomatic young dog with increased total serum bile action values, or in any young dog with hepatic encephalopathy (brain and nervous system damage that occurs as a complication of liver disorders). Symptomatic dogs over two years of age typically acquire a shunt owing to acute or chronic inflammatory, tumor, or toxic liver ailments.
Microscopic features of many disorders causing a lack of fluid in the hepatic portal are similar to hepatoportal microvascular dysplasia. Your veterinarian will perform a liver biopsyfor microscopic examination of liver tissue, aspiration needle biopsies for examination of fluid, and wedge or laparoscopically retrieved samples from the liver.
No specific medical care recommended for asymptomatic dogs. You will need to watch for adverse reactions to drugs. Selected drugs or dietary protein restriction is inappropriate to prescribe. You should not treat the symptoms without first consulting your veterinarian.
Brain and nervous system damage that occurs as a complication of liver disorders and protracted vomiting or diarrhea will need to be treated in hospital for supportive care and diagnostic evaluations; these dogs will most likely have other disorders, or complicated MVD. Mild brain and nervous system damage that occurs as a complication of liver disorders will be controlled with a veterinarian approved protein-restricted diet and appropriate medical treatment,
Recommendations to eliminate MVD from a particular genetic line or breed are not possible at present. Based on information derived from large pedigrees of Yorkshire terriers, Cairn terriers, Tibetan spaniels, Maltese, shih-tzu, and Havanese dogs, breeding unaffected parents does not eliminate MVD from a kindred. The genetic defect involves vascular malformations commonly involving the liver, but may not be limited to this organ. In high incidence kindreds, you will need to remain vigilant for vaguely ill dogs that may have a portosystemic vascular anomaly; surgical exploration can miss this, as can some of the other standard tests.