Canine hepatic microvascular dysplasia/primary hypoplasia of the portal vein (HMVD/PHPV): not the disease that we thought it was!
For many years there has been sparse and confusing information available on HMVD/PHPV. Well, I find it confusing anyway! For starters, although the term PHPV has been chosen by the liver standardisation group of the WSAVA as its preferred terminology, the vast majority of dogs with PHPV don’t have a hypoplastic (main) portal vein: rather they have hypoplasia of the intrahepatic portal vessels. HMVD is a better descriptor: affected dogs often also have proliferation of vessels.
Part of the problem is that primary congenital PHPV may be indistinguishable on histopathology from portal hypoperfusion due to macroscopic portosystemic shunts.
An authority on small animal hepatology tells us:
‘Dogs with microvascular dysplasia have high bile acid concentrations but do not demonstrate clinical illness or other laboratory abnormalities found in dogs with portosystemic vascular anomalies. They do not demonstrate hepatic encephalopathy, do not develop ammonium biurate crystalluria, and typically have a normal protein C activity. A normal lifespan should be expected in dogs with MVD‘
Sharon Center, Oct 2022
After a long interval since the first few publications back in the last century, a 2017 case series sheds more light:
Front Vet Sci. 2017; 4: 224.
Clinicopathological Findings and Prognosis in Canine Cases Diagnosed As Primary Hypoplasia of the Portal Vein
Makoto Akiyoshi, Masaharu Hisasue and Masami Akiyoshi
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5742622/
This study looks at 48 dogs with hepatic disease; of which 28 were diagnosed with PHPV. All were subject to liver biopsy by wedges from > 3 lobes.
It’s noteworthy that PHPV cases in this series included medium-large breeds (1 Golden Retriever, 1 Flat-coat Retriever, 1 Cocker Spaniel)
‘Clinical signs in the PHPV group included gastrointestinal tract signs (9/28; 32.1%), including vomiting, diarrhea, and anorexia; neurologic signs (3/28; 10.7%), including seizures, ataxia, and shivering; and lethargy (2/28; 7.1%). Of the 28 dogs in the PHPV group, two presented with both neurological and gastrointestinal signs. Sixteen of the 28 dogs had no clinical signs other than persistently elevated liver enzymes. In these 16 cases, increased liver enzymes were detected on routine medical examination or on preoperative blood tests for castration/spay. All 28 dogs in the PHPV group had persistently increased liver enzymes for over 2 months.’
…so that’s a somewhat different picture!
Furthermore 5/28 PHPV dogs had a small volume of ascites and acquired portosystemic collaterals with shunting into the left renal vein.
22/28 PHPV dog exhibited raised liver enzymes (ALP 21/28, ALT 13/28)
15/28 had raised pre- or post-prandial bile acids with post-prandial values ranging up to 258 μmol/l.
Low fibrinogen was a feature of 71% of PHPV cases vs 25% of non-PHPV cases (dogs with other liver diseases)
2/28 PHPV dogs, both with acquired shunts, died (600 and 1500 days later) apparently from liver disease with hypoalbuminaemia and hypoglycaemia
16/28 PHPV dogs were asymptomatic and maintained good health in the long term
Several take home messages from this:
- It’s quite common for dogs with PHPV to have raised liver enzymes (especially ALP) but not raised bile acids (although, when bile acids were repeated on multiple occasions all PHPV dogs eventually demonstrated raised level on at least one occasion)
- PHPV may be associated with very marked elevations in bile acids (they aren’t reliably distinguishable from dogs with macroscopic shunts on the basis of degree of elevation)
- A wide range of breeds may be affected including large breeds
- PHPV is commonly a mild or asymptomatic condition but it can also be the cause of a wide range of signs and, occasionally, can drive the development of ascites and multiple acquired shunts. In those cases it may be associated with a significantly more guarded prognosis: sometimes leading to life-threatening complications.
- low fibrinogen may be a useful marker for PHPV
This new framing of the disease helps explain many confusing liver cases we’ve seen over the years!
