Abnormal Bleeding Disorder in Dogs
What is von Willebrand's disease?
Von Willebrand's disease (vWD) is a common, usually mild, inherited bleeding disorder in people and in dogs. It is caused by a lack of von Willebrand factor (vWF), which plays an essential role in the blood clotting process.
Normally the body responds to an injury causing bleeding through a complex defense system. This consists of local changes in the damaged blood vessels, activation of blood cells called platelets, and the coagulation process. A reduction in von Willebrand factor leads to abnormal platelet function and prolonged bleeding times. Affected dogs are prone to bleeding episodes such as nose bleeds, and generally experience increased bleeding with trauma or a surgical procedure.
Von Willebrand’s seldom happens in cats but it is very common in various breeds of dogs. In all, some 60 different purebred breeds have been commonly linked to von Willebrand’s with the Doberman Pinscher having the highest incidence.
Clinical trials conducted on 15,000 Dobermans showed seventy percent of them were carriers of the disease. Of these 15,000 Dobermans, the majority of them didn’t show clinical signs. Another study estimated 68%-73% of Dobermans had the disease
Although Dobermans are the most commonly affected by von Willebrand’s Disease, they usually have the milder forms. It is also one reason Dobermans have such a lower survival rate of diseases such as Parvovirus, which attacks the gastro-intestinal tract and causes bleeding.
Other breeds that have a high incidence of von Willebrand’s disease are:
Often von Willebrand’s will show no clinical signs until the dog begins bleeding for some reason. This reason could be something as simple as a nail trim, spay or neuter or a heat cycle in females or even teething in a puppy. While some dogs never show clinical signs of the disease, others may have nosebleeds or vaginal or penile bleeding. Bleeding from the urinary tract, gums or other mucous membranes and hemorrhaging under the skin are all common symptoms of von Willebrand’s Disease. Females with von Willebrand’s may experience excessive bleeding after whelping (giving birth).
Three forms of the disease are distinguished based on vWF concentration and function. Dogs with Type I vWD (by far the most common) have mild to moderate bleeding abnormalities, depending on the level of vWF. The much rarer types II and III vWD cause severe bleeding disorders.
How is von Willebrand's disease inherited?
Listed below are the breeds for which there is a general consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed. For other breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive.
Bleeding abnormalities are severe in dogs with Types II and III von Willebrand's disease.
Type I vWD, the most common form, is thought to be an autosomal trait with incomplete dominance. This means offspring may inherit the disorder if either parent carries the gene, but not all offspring will be affected to the same extent. Dogs with type I disease have reduced but measurable levels of Von Willebrand factor (1 to 60 per cent). Animals that inherit the gene for type I vWD from both parents (homozygotes) die before birth or shortly thereafter.
The gene for the condition is widespread in the Doberman Pinscher population, and is also relatively common in the Scottish Terrier and Shetland Sheep Dog.
There is an increased risk of the disorder in:
This disease occurs in most other breeds and in mixed-breed dogs as well.
Type II vWD is very rare. It is an autosomal recessive trait. German Short-haired Pointers may be at risk.
Type III vWD is relatively rare. This form is autosomal recessive. Animals are only affected if they inherit the abnormal gene from both parents, who are clinically unaffected carriers. Affected dogs have zero levels of vWF, while carrier parents have 15 to 60 per cent of normal levels. Occurs in the Scottish terrier, Shetland sheepdog, and very sporadically, in the Chesapeake Bay retriever.
What does von Willebrand's disease mean to your dog and you?
Although many dogs are affected by vWD, only a small proportion have severe problems. Dogs with vWD are prone to nose bleeds, bleeding from the gums, and prolonged bleeding during heat or after whelping. There may be prolonged bleeding from the umbilical cord at birth or when your pup sheds its baby teeth. Excessive bleeding after surgery or trauma is common, and may be the first sign of this condition in your dog. You may see blood in your dog's urine or stool.
Most dogs with vWD can lead normal lives, with occasional bleeding episodes that may go unnoticed or can be treated appropriately. Other illnesses, or physical or emotional stress may worsen bleeding episodes. In affected dogs, it is best to consult your veterinarian before using any over-the-counter medications. Drugs such as aspirin for example, alter the function of platelets, and should be avoided in dogs with bleeding disorders.
How is von Willebrand's disease diagnosed?
Because the severity of bleeding with von Willebrand's disease is quite variable, often the disease is not diagnosed until the dog is 3 to 5 years old. Your veterinarian may suspect vWD because of a history of abnormal bleeding in your dog, such as unexplained nosebleeds, or there may be heavy bleeding during surgery. Stillbirths or pups that die shortly after birth ("fading puppies'') may be a result of both parents being carriers of the gene for von Willebrand's disease.
There are specialized tests available to make the diagnosis of von Willebrand's disease. One is a genetic test and the other measures blood levels of von Willebrand factor.
For the Veterinarian
Mucosal bleeding time is the best screening test for a potential defect in platelet function, and is prolonged in dogs with a deficiency in vWF. However the test is non-specific for vWD because it is also prolonged in dogs with thrombocytopenia or functional platelet defects. (Bleeding times are normal in animals with warfarin toxicity, hemophilia A or B, or a deficiency of Factor VII.)
Specific diagnosis of vWD requires either genetic testing in those breeds in which it is available, or vWF measurement. The genetic test is performed by submitting a sample (such as a mucosal scraping) to a genetic testing laboratory. The results are reliable at any age. Measurement of vWF:Ag levels is done by electroimmunoassay or enzyme-linked immunoabsorbent assay (ELISA). Samples for testing must be submitted to the diagnostic laboratory very fresh in a citrate tube (within 1 to 2 hours of collection). Where this isn't possible, the blood sample should be separated immediately after collection and the plasma submitted frozen. It is best to check with your diagnostic laboratory for shipping instructions. VWF levels vary between breeds and with respect to age.
Because of the possible link with hypothyroidism, thyroid status should be evaluated.
For a long time, von Willebrand’s disease, was felt to be associated with hypothyroidism (when a dog borderline for von Willebrand’s factor levels became hypothyroid later in life, the abnormal clotting ability would become evident.) This theory has largely been abandoned but there does seem to be a positive effect when a von Willebrand’s dog is treated with thyroid hormone.
The following breeds have an increased risk of developing hypothyroidism:
For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive. We have listed breeds for which there is a general consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.
What does hypothyroidism mean to you and your dog?
The changes due to gradually decreasing levels of circulating thyroid hormone are slow and insidious. Early signs (which are usually not recognized as being related to hypothyroidism) include lower energy levels and increased susceptibility to infections.
As the disease progresses, you will likely notice changes in your dog's hair coat - symmetrical hair loss with or without darkening of the skin, and dry or greasy hair. Other signs of hypothyroidism include a slow heart rate, lethargy, mental dullness, intolerance to cold, infertility in males and females, constipation, and weight gain.
Less commonly, a dog with hypothyroidism may experience heart disease, a bleeding disorder, profound muscular weakness associated with abnormalities in the muscles or nerves, or another endocrine disorder such as diabetes mellitus.
Thyroid hormones are essential for normal growth and maturation of the nervous and skeletal systems. Puppies with congenital hypothyroidism will have stunted growth as well as many other abnormalities. Severely affected puppies most likely die before weaning.
How is hypothyrodism diagnosed?
Because there is such a broad range of possible clinical signs, hypothyroidism can be quite difficult to diagnose. Blood tests may show certain suggestive (but non-specific) abnormalities. If your veterinarian suspects this condition, s/he will perform laboratory tests to assess thyroid function.
For the Veterinarian
How is hypothyroidism treated?
The standard treatment is levo-thyroxine given once a day. This must be continued for life. Within a week of starting treatment, your dog's attitude and activity levels should improve. It can take up to 6 weeks before there is noticeable improvement in the skin and haircoat, but eventually all abnormalities should completely resolve.
Dogs on thyroid replacement can live a normal life. Your veterinarian will monitor thyroid hormone levels periodically and adjust the dose if required. Certain other illnesses may also necessitate dosage adjustment.
Congenital hypothyroidism is treated the same way. Clinical signs are usually completely reversed with subsequent normal physical and mental growth and development, as long as the condition is recognized and treatment started very early (3 to 4 months of age).
Although inheritance of this disorder has not been determined, it is advisable not to breed affected dogs. The OFA (Orthopedic Foundation for Animals) maintains a thyroid registry based on assessment of FT4, cTSH, and TgAA, which is useful for breeders attempting to choose dogs free of hypothyroidism for a breeding program.
How is von Willebrand's disease treated?
This condition cannot be cured but it can be managed. Your veterinarian will discuss this with you when the diagnosis is made.
You will likely be able to control mild bleeding yourself by applying prolonged pressure. In other circumstances, veterinary care such as cautery or sutures may be required. Severe bleeding episodes are treated by administering a source of von Willebrand factor through a transfusion. If your dog requires surgery, your veterinarian may recommend a transfusion pre-operatively as a precaution, depending on the severity of the bleeding disorder, and the type of surgery.
Thyroid supplements may help to control bleeding, if your veterinarian determines that your dog is hypothyroid.
For the Veterinarian
Exogenous vWF may be supplied through administration of fresh whole blood, fresh or fresh-frozen plasma, or cryoprecipitate (treatment of choice).
Where possible, avoid the use of drugs that have been known to cause thrombocytopenia or otherwise affect platelets. Such drugs include NSAIDs (aspirin, phenylbutazone, ibuprofen, indomethacin), some antibiotics (penicillin, sulfonamides, ampicillin, chloramphenical), antihistamines, phenothiazines, theophylline,heparin, and estrogen
Some studies have shown that thyroid supplementation in euthyroid dogs can reduce bleeding, but other studies have contradicted this.
The trait for von Willebrand's disease is widespread, particularly in Doberman pinschers but also in several other breeds. An accurate genetic test has been developed for the Doberman Pinscher, Scottish Terrier, Shetland Sheepdog, Manchester Terrier, Poodle, and Pembroke Welsh Corgi.
Testing can reliably identify dogs with vWD, dogs that are carriers, or dogs that are clear (see reference below for information on testing).
In breeds where specific genetic tests are not yet available, carriers of the trait can still be identified through the blood test for von Willebrand factor. These dogs have reduced levels of vWF (25 to 60 per cent) but do not have bleeding problems. Levels vary with age and between breeds.
Where a bleeding disorder has been identified, breeders are advised to test breeding stock. Dogs with von Willebrand's disease and those who are carriers should not be used for breeding.