Overview of Von Willebrand's Disease (VWD) in Dogs
Von Willebrand's disease (vWD) is caused by a deficiency of von Willebrand's factor (vWF), one of the elements that allow blood to form clots. Von Willebrand's disease can cause prolonged or excessive bleeding in dogs.
VWD is a hereditary defect that is passed from parents to offspring through genetic material. Inheritance is complicated, but vWD is equally likely to affect males and females, and one affected parent can pass the condition to his offspring. Many different dog breeds can be affected with vWD and different breeds are prone to different subtypes of the disease.
The severity of vWD varies from dog to dog, but in most, it becomes a problem only when surgery is needed or if the dog is injured.
What to Watch For
Symptoms of Von Willebrand's Disease (VWD) in Dogs may include:
- Prolonged or excessive bleeding after injury
- Prolonged or excessive bleeding after surgery
- Bleeding from the gums or nose
- Bloody urine
Diagnosis of Von Willebrand's Disease (VWD) in Dogs
VWD cannot be diagnosed definitively with routine in-hospital testing but requires specialized tests. Diagnostic tests are needed to recognize vWD and exclude other diseases. These tests may include:
- A complete medical history and physical examination
- Complete blood count (CBC). This test should be performed on any bleeding dog to be certain the number of platelets (the cells which allow clots to form) is normal and to check for anemia, a deficiency of oxygen-carrying red blood cells.
- Tests of clotting ability, including activated partial thromboplastin time (APTT) and one-stage prothrombin time (OSPT). Although results of these tests will be normal in a dog with vWD, they help rule out other diseases.
- Buccal mucosal bleeding time. In this crude test of platelet function, vascular (blood vessel) function, and vWD, a small, precise cut is made inside the dog's lip and the time it takes to form a clot is measured. This test helps your veterinarian decide if more specific testing is indicated.
- Measurement of von Willebrand's factor. Unfortunately, this specific blood test may need to be repeated because there is a lot of day-to-day variation in vWF concentration and because results may fall into a borderline range.
Treatment of Von Willebrand's Disease (VWD) in Dogs
- Most dogs with vWD require no treatment unless a surgery is planned or an injury is sustained.
- Blood products from healthy dogs can stop excessive bleeding in dogs with vWD. Either the liquid part of blood (plasma), whole blood (plasma plus blood cells) or a concentrate of clotting factors (cryoprecipitate) may be given.
- If repeated transfusions are necessary, it is important to cross match the patient's blood with the donor's blood.
- Desmopressin acetate (DDAVP) is a hormone that can increase von Willebrand's Factor concentrations temporarily. It may be given just prior to surgery or to a healthy dog that will then be used to give blood to the dog with vWD.
- If a dog with vWD is found to have poor thyroid function, thyroid supplementation is recommended.
Home Care and Prevention
Provide soft padded areas for your dog to lie on. Minimize the chance of injury by observing and fixing any sharp corners, such as on doggie doors. It is usually not necessary to limit activity as spontaneous bleeding is not common. If your dog should begin bleeding, seek veterinary assistance immediately.
Because it is a hereditary disease, an animal born with vWD cannot be cured. Do not breed dogs that have vWD. Although careful breeding can minimize the incidence of vWD, a complex inheritance pattern makes elimination of the disease in a breed difficult.
Minimize the chance of injury by keeping your dog confined either in a fenced area or on a leash when outdoors. If your dog should begin bleeding, seek veterinary assistance immediately.
Inform any veterinarian treating your dog about his vWD. This is especially important prior to surgical procedures. Inform any groomer handling your dog about his condition; they will use extra care in clipping and trimming nails and can be prepared if a cut occurs.
In-depth Information on Canine Von Willebrand's Disease (VWD)
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.
In-depth Information on Diagnosis of Von Willebrand's Disease (VWD) in Dogs
Diagnostic tests are needed to recognize vWD and exclude other diseases. Tests may include:
- A complete history and physical examination. Breed, age and prior illness will be questioned.
- A dog's breed will be considered if your veterinarian suspects vWD. Although any breed can be affected, certain breeds, such as the Doberman pinscher, Shetland sheepdog, schnauzer and golden retrievers are more likely to have vWD. German shorthaired and wirehaired pointers, Scottish terriers and Chesapeake Bay retrievers have been documented to have very rare but very severe forms of vWD.
- A dog's age will be considered if vWD is suspected. Because this is a congenital disease (present from birth), dogs are often identified at the time of neutering or during early cosmetic surgery (ear cropping). Nonetheless, it is not uncommon for a dog with mild vWD to go undetected until later in life.
- A complete medical history can lead your veterinarian to suspect vWD. A previously healthy dog that experiences prolonged bleeding after minor injury is a typical example of vWD. Certain rare forms of vWD can result in severe, life-threatening bleeding unassociated with injury.
- A physical examination may prompt your veterinarian to consider vWD as a cause for abnormal bleeding. The type and location of bleeding may make platelet disorders, hemophilia or rodenticide intoxication more or less likely a cause of bleeding. Physical examination may also rule local disease out as a cause of bleeding.
- A complete blood count (CBC) should be performed on any bleeding dog to make certain the number of platelets is normal and to check for anemia (a deficiency of oxygen-carrying red blood cells).
- Tests of clotting ability, including Activated Partial Thromboplastin Time (APTT) and One-Stage Prothrombin Time (OSPT), may be requested in a bleeding dog. Although results of these tests will be normal in a dog with vWD, they help rule out other diseases, including hemophilia, warfarin toxicity (rat bait poisoning) and disseminated intravascular coagulation.
- Buccal mucosal bleeding time is a screening test for vWD. A small, precise cut is made inside the dog's lip and the time it takes for a blood clot to form is measured. In dogs with vWD the time until a clot forms will be longer than normal. In addition to vWD, platelet deficiency or dysfunction and blood vessel disease may prolong bleeding times.
- Specific testing involves sending blood samples to have vWF measured. The amount of vWF in the blood sample is compared to a pooled sample from a large group of healthy dogs. The results are expressed as a percentage of the normal pooled sample (exact percentages considered to constitute each range may vary slightly from laboratory to laboratory). If a dog is found to have greater than 70 percent as much vWF as the pooled sample, it is considered unaffected. Dogs with less than 50 percent of the amount of vWF in the pooled sample are considered to be affected. Dogs with 50 to 69 percent of the amount of vWF found in the pooled sample fall into a “borderline” range. von Willebrand's disease occurs in three subtypes. Type I vWD is by far the most common and the least severe. Types II and III vWD are relatively rare but cause much more severe bleeding episodes than Type I vWD.
- Unfortunately, repeated measurement of vWF concentrations may be necessary, especially if the dog's values fall into the “borderline” range. There is considerable day-to-day variation in blood vWF concentrations. Factors like pregnancy, exercise, stress or illness can affect concentrations.
- In dogs believed to have the rare but severe form of vWD known as Type II vWD, electrophoresis can be used to measure the size of the vWF present. Type II vWD, found most often in German shorthaired and wirehaired pointers, is associated with a loss of only the large pieces of vWF.
- Genetic testing for vWD is available for some breeds of dog, including Doberman pinschers, Scottish terriers, poodles, Manchester terriers, Shetland sheepdogs and Pembroke Welsh Corgis.
- If vWD is identified, your veterinarian may request testing for thyroid hormone status. An underactive thyroid gland (hypothyroidism) has been associated with vWD in some cases, and although controversial, correction of hypothyroidism may improve the vWD.