Clinical Pathology Case Study: Microvascular dysplasia in a dog

Follow up diagnostic tests and interpretation

Given the results above, a bile acids panel was performed and plasma protein C levels were measured. 

Interpretation: Results are suggestive of microvascular dysplasia (MVD).

Discussion

Microvascular dysplasia (MVD) is a vascular anomaly found in small breed dogs and in particular in terrier type breeds. It is a polygenic disease and has a vast clinical presentation. The degree of vascular change is extremely variable and this accounts for the markedly different clinical presentations. Dogs that are severely affected will sometimes have clinical signs as puppies up to and including hepatic encephalopathy. Some will also have concurrent portosystemic shunts (PSS). 

There is a large percentage of affected dogs who are diagnosed when being screened for elective surgery. Others are diagnosed based on abnormal bile acids done when they are being screened for pre breeding health checks. These dogs may live a long and healthy life and yet others will present with evidence of liver dysfunction. These dogs may be perfectly normal until they are adults or even in their senior years and there is loss of liver mass/function secondary to other disease. 

The diagnosis of MVD requires a biopsy to be definitive but there is a test that can be done to aid in differentiating from PSS. This is an important differentiation as MVD cannot be surgically corrected but needs to be medically managed. Plasma protein C is a coagulation protein. In most dogs with MVD this value is usually within the normal reference interval, as it is in this case. In dogs with portosystemic shunts the Protein C level is decreased. 

Clinical signs and changes in laboratory work noted with MVD are similar but often milder than those seen with PSS - low urea, low mean cell volume (MCV), low albumin and possible changes in liver enzymes. Other dogs with MVD will be completely normal clinically and on blood work, but will have a significant abnormality in their bile acids panel. 

Yorkshire Terriers were one of the first breeds to be listed as being prone to this. Now it is considered a differential in many other small breed dogs.