Understanding the Difference Between Microvascular Dysplasia and Portosystemic Shunts in Dogs
Liver-related vascular abnormalities in dogs can be confusing, particularly when trying to differentiate between
microvascular dysplasia (MVD) and
portosystemic shunts (PSS). Both conditions affect liver function by altering normal blood flow, but they differ significantly in their nature, diagnosis, and treatment approaches. This article explores the key differences, clinical implications, and treatment strategies for both conditions, aiming to provide clarity for concerned pet owners.
What is Microvascular Dysplasia (MVD)?
Microvascular dysplasia, also referred to as
portal vein hypoplasia, is a congenital condition in which the microscopic portal veins in the liver are underdeveloped or absent. This affects the liver’s ability to receive proper blood flow, essential for detoxification, metabolism, and protein synthesis. MVD is most common in
small dog breeds like Yorkshire Terriers, Maltese, and Shih Tzus.
What is a Portosystemic Shunt (PSS)?
A
portosystemic shunt is a larger, visible vascular malformation where blood bypasses the liver completely by traveling from the portal vein directly into systemic circulation, skipping liver filtration. Shunts may be congenital or acquired and pose serious functional impairments for the liver.
Key Differences Between MVD and PSS
- Size and visibility: MVD affects microscopic vessels, requiring biopsy for confirmation, while PSS involves larger vessels detectable via imaging.
- Diagnosis complexity: MVD diagnosis typically involves exclusion of a macroscopic shunt through imaging along with liver biopsy, whereas PSS is often confirmed directly by imaging techniques.
- Presence of clinical signs: MVD often presents with mild or no symptoms, while PSS can cause severe symptoms including neurological issues, behavioral changes, and systemic metabolic disturbances.
- Treatment approach: MVD is managed medically with diet and supplements; shunts often require surgical correction.
- Prognosis: MVD usually has a favorable outlook with many dogs living normal lives, while PSS may lead to more complications if untreated.
Symptoms to Watch For
Both conditions may show similar signs, though often milder in MVD:
- Poor growth or weight gain
- Gastrointestinal symptoms like vomiting or diarrhea
- Pica (eating non-food items)
- Increased thirst and urination
- Urinary tract infections or stones
- Neurologic signs (especially in PSS): head-pressing, ataxia, seizures
Diagnostic Methods
A series of tests help differentiate MVD from a shunt:
- Serum bile acid test: Measures pre- and post-meal bile acids. MVD typically shows mild to moderate elevation, PSS shows more dramatic spikes.
- Protein C activity: Normal in MVD (>70%), reduced in PSS.
- Imaging: Ultrasound, CT, MRI, or scintigraphy to detect or exclude large vascular malformations.
- Liver biopsy: Required for confirming MVD. Multiple samples from various lobes improve accuracy.
Treatment Options
MVD Management:
- No treatment needed for mild or asymptomatic cases.
- Medical therapy for dogs with more severe signs or hepatic encephalopathy:
- Low-protein, high-quality hepatic diets
- Lactulose to reduce ammonia absorption
- Short-term antibiotics (e.g., metronidazole)
- Hepatoprotective supplements (e.g., SAMe, milk thistle)
PSS Treatment:
- Surgical correction of the shunt is often recommended.
- Pre- and post-surgical dietary and medical support similar to MVD protocols.
Prognosis and Lifespan
Dogs with MVD often experience no progression of disease and lead long, healthy lives. PSS prognosis varies depending on response to surgical treatment and presence of neurological complications.
Breeding Considerations
Breeding dogs diagnosed with MVD is strongly discouraged due to its suspected hereditary component. Genetic screening may help in reducing breed prevalence.
Conclusion
While both
microvascular dysplasia and
portosystemic shunts result in impaired liver function, they differ significantly in anatomy, severity, and treatment strategies. Early diagnosis through laboratory and imaging tests, combined with careful management, can ensure good quality of life for affected pets. Speak with your veterinarian if your dog shows any signs related to liver dysfunction, especially if they are a small breed predisposed to these conditions.
