Von Willebrand disease (vWD) 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. Many dogs with this disorder never show symptoms, which include spontaneous bruising and bleeding or excessive bleeding after an injury or surgery, and are mostly unaffected by the disease, but for dogs with more serious cases, heavy bleeding can lead to death if not treated promptly.
Although any dog potentially can have vWD, certain breeds, including Doberman pinschers, Airedales, Scottish terriers, and poodles, are more prone to this hereditary disorder.
What Is von Willebrand Disease?
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 (vWF). 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.
Dogs with von Willebrand disease have either insufficient vWF, defective vWF, or absent vWF.
Symptoms 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. Affected dogs may also bruise severely in response to even minor trauma or spontaneously.
Dogs with von Willebrand disease may live seemingly normal lives for years before showing signs of the disorder, and some never display obvious symptoms at all. For many, the condition is discovered during a routine veterinary checkup or a visit for another issue. Minor cuts and scrapes might not bleed excessively because other clotting factors may be able to handle minor injuries to blood vessels.
With some dogs, symptoms appear during a surgery, often a spay or neuter, when the dog bleeds more heavily during the procedure than would be expected. Once treated however, and healed from the surgery, the dog might not have another bleeding episode.
In other dogs with 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, however, excessive bleeding may occur in puppies while they are teething.
Dogs that do have symptoms of vWD generally bleed from mucus membranes, including the nose, gums, and reproductive organs. Some have digestive system bleeding, leading to bloody stools or urine. Spontaneous bruising, or bruising in response to a minor injury, is common, although it can be difficult to spot bruises on dogs with thick or long fur.
Causes of von Willebrand Disease
There are three identified types of von Willebrand disease in dogs. Each involves a varying degree of deficiency of von Willebrand factor. Certain breeds of dog are more susceptible than others to each type of the disease.
Type 1: Dogs with Type 1 vWD have all the proteins that make up von Willebrand factor, but they lack a sufficient amount for effective clotting. Type 1 is the most common form of von Willebrand disease and is seen in several dog breeds, including 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. This is the least severe form of the disease.
Type 2: 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, at times even without known trauma.
Type 3: 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 at 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 tests 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." 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. Note that a dog with a borderline test might carry the genetic tendency towards the disorder, and yet not have any abnormal bleeding itself. Dogs with abnormal results do carry the genetic tendency towards the disease, and often also have abnormal bleeding themselves.
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, including aspirin, certain types of antibiotics, or heparin.
There is a pretreatment option 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, although 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 prior to a necessary surgery. This releases vWF into the bloodstream and temporarily shortens the bleeding time. Not all dogs will respond to DDAVP, however.
Prognosis for Dogs With von Willebrand Disease
Your dog's prognosis depends a great deal on the type of vWD it has, as well as whether or not severe bleeding episodes occur. As a general rule, dogs with type 1 vWD have a better prognosis than those with type 2 or type 3, and many dogs with type 1 lead normal lives.
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.
How to Prevent von Willebrand Disease in Dogs
It is important for the breeders of dogs at risk for vWD 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.