Von Willebrand disease is a hereditary bleeding disorder that is characterized by a deficiency of von Willebrand factor, a specific protein needed to help clot blood. Sometimes called pseudohemophilia, vWD is the most common inherited bleeding disorder in both dogs and humans.
What is von Willebrand Factor?
In a normal dog, the blood clots (coagulation) and stops blood flow (hemostasis) in response to trauma to blood vessels. While it may seem like a basic function, blood clotting is actually a very complicated process.
When coagulation begins, blood cells called platelets clump together. These platelet clumps then adhere to the cells along the walls of the blood vessels to form a clot. Think of this as plugging the hole in the vessel. There are substances in the blood plasma called clotting factors that facilitate the process of coagulation and hemostasis. Among these substances are glycoproteins called von Willebrand factor (named after Dr. Erik von Willebrand who discovered the substance due to his own disorder). During clotting, von Willebrand factor is essential to bond platelets to the cell wall by creating fibrin, a kind of cellular mesh that seals the blood vessel. Von Willebrand factor works with clotting factor VIII to form fibrin.
Signs of von Willebrand Disease in Dogs
When a dog does not have enough von Willebrand factor, the blood cannot clot properly. This can lead to prolonged and sometimes uncontrollable bleeding when a blood vessel is broken. Bleeding can be caused by an unexpected injury or even routine surgery. In some cases, bleeding occurs spontaneously from the GI tract, urinary tract, gums, and/or nasal cavity.
Dogs with von Willebrand disease may live seemingly normal lives for years before showing signs. Minor cuts and scrapes may not bleed excessively because other clotting factors may be able to handle minor injuries to blood vessels. Often, symptoms appear during the first surgery. This is often a spay or neuter.
In mild cases of vWD, bleeding issues do not appear until later in life after the disease is worsened by other disorders, such as hypothyroidism. In the most severe cases, excessive bleeding may occur in puppies while they are teething.
Types of von Willebrand Disease in Dogs
There are three identified types of von Willebrand disease in dogs. Each involves a varying degree of deficiency of von Willebrand factor.
Dogs with Type 1 von Willebrand disease have all the proteins that make up von Willebrand's factor, but they lack a sufficient amount for effective clotting. Type 1 is the most common form of von Willebrand disease. This form is most often seen in Doberman Pinschers, German Shepherd Dogs, Standard Poodles, and Shetland Sheepdogs. However, type 1 vWD may be present in other breeds or mixed-breed dogs. Many dogs with type 1 vWD show no symptoms until they undergo surgery or experience a trauma.
Dogs with type 2 vWD have a normal level of von Willebrand factor, but the proteins are structurally or functionally defective. Type 2 is typically seen in German Wire-Haired and Short-Haired Pointers. Dogs with type 2 vWD can experience severe bleeding episodes, even sometimes if no known trauma has occurred.
Dogs with type 3 vWD are completely missing vWF. This form is most often seen in Shetland Sheepdogs, Scottish Terriers, and Chesapeake Bay Retrievers. Type 3 is the most severe form of vWD.
A dog may also be a genetic carrier of von Willebrand disease but not experience symptoms.
Diagnosing von Willebrand Disease in Dogs
In many cases, it is not known that a dog has von Willebrand disease until an episode of spontaneous or uncontrollable bleeding occurs. If your dog is a breed that is predisposed to vWD, testing is a good idea. This is especially important before any kind of surgery is performed. Talk to your vet about the testing options so you can be prepared.
There are several bleeding disorders in dogs, so a bleeding episode alone is not enough to diagnose vWD. If your dog has had an episode of excessive bleeding, then testing should be done as soon as your dog is stabilized to determine the cause of the bleeding.
First, a complete blood count should be done to look and all blood cells and determine if they are normal. Dogs with vWD often have normal CBCs unless they have recently been bleeding.
A timed clotting test called buccal mucosal bleeding time is a quick and sometimes useful tool in diagnosing bleeding disorders. The BMBT test involves making a small prick in a dog's gum and timing how long it takes to form a visible clot. This may be done while a dog is under anesthesia prior to surgery. A prolonged clotting time indicates some kind of clotting abnormality, but it cannot specifically diagnose vWD. Additionally, BMBT is not always prolonged in dogs with vWD, so this is not a definitive test for vWD.
Other tests to determine bleeding time include activated clotting time and PT/PTT. These will have normal results in dogs with vWD. However, it is important to run these test to rule out other bleeding issues.
The primary way to determine the presence of vWD is to run a von Willebrand factor antigen assay, or vWF:Ag%. These levels may fluctuate throughout the day, so there are a few ranges to consider. Normal dogs will have a result of 70 to 180. A dog is considered borderline at a result of 50 to 69. Abnormal results range from 0 to 49.
DNA testing is another way to determine if a dog will be affected by vWD. This can also reveal if a dog is a carrier of vWD. This DNA test for vWD is only available for certain dog breeds and can be performed by a lab such as VetGen.
Treatment Options for Dogs with von Willebrand Disease
If the dog with vWD is actively bleeding, steps must be taken to try and control blood loss. If the bleeding is minor to moderate, it may be possible to stop bleeding with bandages or other means of pressure.
When bleeding occurs during surgery, the vet will attempt to ligate vessels (stitch them up) as fast as possible. A dog with significant blood loss will need a blood transfusion. Vets also take precautions to avoid any drugs that can further prolong bleeding or affect clotting mechanisms.
There is a pre-treatment option of dogs if the presence of vWD is known prior to surgery and the surgery is considered necessary (meaning the benefits are deemed to outweigh the risks). The veterinarian can administer cryoprecipitate, a blood product that is rich in von Willebrand factor. If cryoprecipitate is not available, plasma is an alternative (though it does not contain as much von Willebrand factor. These blood products can temporarily provide the dog with the vWF needed to form blood clots during surgery.
For dogs with mild vWD (particularly Type 1), vets may administer a hormone called desmopressin acetate, or DDAVP. This releases vWF into the bloodstream and temporarily shortens the bleeding time. Not all dogs will respond to DDAVP. Many vets consider this treatment controversial or ineffective.
How to Prevent von Willebrand Disease in Dogs
The best thing that can be done to protect dogs from von Willebrand disease is to prevent them from being born with it in the first place. It is important for the breeders of dogs at risk to screen their dogs prior to breeding. A dog with abnormal results should never be bred. Any dog with a hereditary health problem should be spayed or neutered in order to protect future generations of dogs.
Fortunately, dogs with mild to moderate vWD can often live normal lives. Knowing your dog has the disease prior to surgery is the best way to protect against bleeding episodes. Dogs with severe vWD should be monitored to prevent injuries and to detect spontaneous bleeding as soon as possible. These dogs may need to undergo blood transfusions periodically to treat blood loss.
What to Do If Your Dog Has Von Willebrand Disease
If you have learned that your dog has von Willebrand disease, it's important to find a veterinarian you trust and stay in close communication about your dog's needs and ongoing condition. It's a good idea to keep a list of nearby emergency hospitals available in case a bleeding episode occurs. If your dog has a bleeding episode, head to the nearest open veterinarian as soon as possible. Also, remember to communicate with any new vets or vet staff about your dog's vWD status. This will enable them to keep your dog safe and avoid treatments or procedures that may cause harm.