Understanding Microhepatica in Dogs: Causes, Diagnosis, and Management
Microhepatica, or a small liver, in dogs is often a visible indicator of an underlying condition called hepatic microvascular dysplasia (MVD). This congenital disorder involves abnormalities in the liver's microscopic blood vessels—specifically, the portal veins that are crucial for carrying blood rich in nutrients from the gastrointestinal tract into the liver. In MVD, these tiny portal veins are either underdeveloped or completely absent, resulting in a smaller liver with compromised function.
What Causes Microhepatica?
The primary cause of Microhepatica in dogs is congenital hepatic microvascular dysplasia (MVD), also known as portal vein hypoplasia. This condition is often inherited and most prevalent among certain small dog breeds. The liver becomes small because it receives inadequate nutrient-rich blood supply required for normal growth and metabolic activity. In the absence of sufficient perfusion, the liver may atrophy or fail to develop properly.
Breeds Predisposed to MVD
- Yorkshire Terriers
- Cairn Terriers
- Maltese
- Miniature Poodles
- Shih Tzus
- Lhasa Apsos
- Cocker Spaniels
- West Highland White Terriers
- Dachshunds
- Bichon Frises
Though rare, MVD has also been reported in larger breeds and cats.
Clinical Signs of MVD
MVD may produce no obvious signs in some dogs, while others may display a variety of clinical symptoms:
- Small stature or poor growth
- Vomiting and diarrhea
- Poor appetite
- Pica (ingesting non-food items)
- Increased thirst and urination
- Blood in urine or urinary tract infections
- Neurologic signs (head-pressing, ataxia, seizures, behavioral changes)
In many cases, the clinical signs are milder compared to dogs with macroscopic portosystemic shunts (PSS).
Diagnostic Approach
Diagnosing MVD involves a combination of laboratory testing, imaging, and histopathological examination:
- Blood tests: May reveal mild anemia, decreased albumin, BUN, glucose, and elevated liver enzymes.
- Urinalysis: May show dilute urine or ammonium biurate crystals.
- Serum bile acid test: Pre- and post-meal tests may show mildly elevated bile acids.
- Protein C activity: Usually normal in MVD but decreased in PSVA.
- Imaging: Abdominal ultrasound, CT, MRI, or nuclear scintigraphy may help rule out macroscopic shunts and identify a small liver.
- Liver biopsy: Confirms diagnosis by showing characteristic microscopic vascular changes. Multiple samples from different liver lobes improve accuracy.
Treatment and Management
MVD is usually nonprogressive, meaning that many dogs live normal lifespans without treatment. However, management is required when clinical signs are present. Treatment focuses on controlling the metabolic and neurological effects that can arise from reduced liver function:
- Dietary protein restriction using highly digestible sources (e.g., dairy, soy)
- Prescription hepatic diets
- Lactulose to reduce intestinal ammonia absorption
- Antibiotics (e.g., metronidazole) to manage intestinal bacteria
- Hepatoprotective supplements such as vitamin E, SAMe, silymarin, ursodeoxycholic acid
- Probiotics and yogurt to promote gut health (effectiveness unclear)
Monitoring and Prognosis
Most dogs with MVD do not deteriorate significantly over time. Regular monitoring of:
- Liver enzymes
- Blood protein levels
- Blood ammonia concentrations
is recommended. Breeders and pet owners should avoid retesting bile acids frequently if the dog is otherwise healthy. Owners should also be vigilant for new symptoms or secondary complications such as urinary stones.
Breeding Considerations
Because MVD is believed to be hereditary with a likely polygenic inheritance pattern, breeding affected dogs—even those without apparent clinical signs—is strongly discouraged. Even asymptomatic carriers can pass on the condition to their offspring. Genetic testing is necessary for effective breeding decisions.
Conclusion
Hepatic microvascular dysplasia is a significant cause of microhepatica in dogs, especially small breeds. While often asymptomatic, it can produce a range of clinical signs and affect the liver's metabolic function. With proper diagnosis and, when necessary, medical management, most dogs with MVD live full and happy lives. Responsible breeding and regular veterinary monitoring are crucial elements in managing this condition long term.
