Understanding the Onset and Development of Microvascular Dysplasia (MVD) in Dogs
Hepatic microvascular dysplasia (MVD), also referred to as portal vein hypoplasia, is a
congenital liver condition in dogs characterized by
underdeveloped or absent microscopic blood vessels within the liver. This anomaly disrupts normal hepatic blood flow, which can impact liver function in metabolizing toxins, synthesizing proteins, and maintaining metabolic balance.
When Do Dogs Develop MVD?
Because MVD is a
congenital disorder, dogs are typically born with it. However, the manifestation of
clinical signs can vary significantly based on the severity of the vascular abnormality. While some dogs may show signs early in life, others remain asymptomatic or display subtle symptoms only later.
- Most cases are diagnosed in puppies or young dogs during routine testing or due to mild abnormalities picked up incidentally.
- Some dogs may present with delayed growth, poor weight gain, or gastrointestinal upset within the first year of life.
- Others may go undiagnosed for years due to the nonprogressive nature of the condition in many individuals.
Breeds Most Commonly Affected
MVD occurs most frequently in
small breed dogs, suggesting a genetic predisposition. Breeds with higher prevalence include:
- Yorkshire Terriers
- Cairn Terriers
- Maltese
- Miniature Poodles
- Shih Tzus
- Lhasa Apsos
- Cocker Spaniels
- West Highland White Terriers
- Dachshunds
- Bichon Frises
Large breed dogs and cats are less commonly affected, although isolated feline cases have been reported in literature.
Signs and Symptoms Associated with MVD
Clinical presentation in dogs with MVD ranges from
no visible symptoms to more noticeable impairment in liver function. When symptoms are present, they typically include:
- Stunted growth or poor weight gain
- Lethargy or reduced activity levels
- Neurological signs such as head-pressing, seizures, or behavior changes (in rare cases)
- Increased thirst and urination
- Vomiting, diarrhea, or decreased appetite
- Urinary issues such as infections or blood in urine
More often than not, signs are
milder than those seen with large portosystemic shunts, which makes diagnosis more challenging.
Diagnostic Approaches
Veterinary diagnosis of MVD involves a combination of methods due to the subtlety of clinical signs:
- Blood Biochemistry: May show mild anemia or reduced albumin, glucose, and BUN.
- Urinalysis: Can reveal dilute urine or ammonium biurate crystals.
- Serum Bile Acids Testing: Mildly to moderately elevated postprandial bile acids can indicate MVD.
- Protein C Testing: Normal levels help differentiate MVD from portosystemic vascular anomalies.
- Imaging (Ultrasound, CT, MRI): Used to assess liver size and exclude large shunts.
- Liver Biopsy: Essential for confirming characteristic microscopic changes.
Multiple liver samples taken from different lobes improve diagnostic accuracy, while needle biopsies are discouraged due to their small sample size.
Treatment and Long-Term Management
Most dogs with MVD do
not require aggressive treatment and can lead normal lives with minimal or no intervention. Management depends on the severity of the condition:
- Asymptomatic Dogs: No treatment or dietary changes usually needed.
- Symptomatic Dogs: Managed medically, focusing on liver support.
Recommended treatments include:
- Dietary changes: Low-protein or prescription hepatic diets (high-quality protein sources)
- Lactulose: Reduces ammonia absorption in the gut
- Antibiotics: Short-term use, such as metronidazole, to control intestinal bacteria
- Hepatoprotective supplements: SAMe, vitamin E, silymarin
- Probiotics and yogurt: May support gut health (efficacy uncertain)
Monitoring and Prognosis
Ongoing medical evaluations are important for tracking liver function and catching potential complications. Regular checks may include:
- Bloodwork to monitor liver enzymes
- Protein levels
- Ammonia concentrations
Most affected dogs maintain a good quality of life with appropriate management.
Breeding Considerations
Due to
MVD’s suspected hereditary basis, breeding affected dogs is not recommended. The condition appears to follow a
polygenic inheritance pattern, meaning even clinically normal parents can produce affected offspring.
Conclusion
MVD is a
nonprogressive congenital liver condition present from birth, especially in small-breed dogs. Although clinical signs may not develop until later or may remain mild, vigilant monitoring and appropriate management allow most dogs to thrive. Informed breeding choices and early detection are key to minimizing the impact of this under-recognized but widespread condition.
