Von Willebrand’s Disease (VWD)

Von Willebrand’s Disease (VWD)

By: Dr. Leah Cohn

Section: Information In-depth

An analogy can be made between the body's natural ability to stop bleeding (coagulation) and the application of a bandage to stop bleeding. The "gauze" of the bandage is formed by the aggregation, or clumping, of blood cells called platelets. The "tape" that holds the "gauze" in place is formed by triggering soluble coagulation factors in the blood to solidify on the clumped platelets. von Willebrand's factor, which is deficient in dogs with vWD, is partially responsible for the clumping of the platelets. von Willebrand's disease is only one of many potential causes of excessive or prolonged bleeding in the dog. Other causes of bleeding may include:

  • Thrombocytopenia is a deficiency of platelets, the cells that allow the blood to clot.
    Thrombocytopenia can be due to inadequate production of platelets in the bone marrow, destruction of platelets in the blood vessels, excessive use of platelets or sequestration of platelets in organs like the spleen.

  • Thrombocytopathy is a defect in platelet function. In order to stop bleeding, platelets must stick to the inside of a torn blood vessel, then stick to each other. Sometimes, even if there are adequate numbers of platelets, the platelets aren't sticky enough and cannot form a clot.

  • Hemophilia is an inherited deficiency in one of several soluble coagulation factors; each deficiency has its own unique name. Although the platelets can clump normally in hemophilia, the platelet clump doesn't stay in place and bleeding results.

  • Warfarin intoxication is poisoning by a common ingredient in rodent bait. Currently available rodent baits often contain ingredients that have the same effects as warfarin but are much more potent and longer lasting. These poisons affect vitamin K metabolism and prevent the proper activity of soluble coagulation factors.

  • Disseminated intravascular coagulation (DIC) is not a primary disease, but rather a consequence of disease. Many types of severe illness cause DIC, causing tiny blood clots throughout the body. As a result, both platelets and soluble coagulation factors are used up. Abnormal and excessive bleeding is the consequence.

  • Vasculitis is disease of the blood vessels themselves. Abnormal blood vessels are weakened and often have small holes in the lining, allowing abnormal bleeding to occur. Vasculitis can be a consequence of infection, cancer or an attack on the vessels by the animal's own immune system (immune-mediated disease).

  • Localized disease processes can result in a tendency to bleed. For instance, severe gum disease can cause oral bleeding; nasal tumors or fungal infection of the nose can cause nosebleeds. Kidney or bladder stones can cause urinary bleeding.

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