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Name
Von Willebrand's Disease, Canine
Short Description
Canine von Willebrand's disease
Affected Animals: Dogs of many breeds can be affected with von
Willebrand's disease. Some breeds have a higher incidence than
others, including Doberman pinschers, Scottish terriers, Airedales,
basset hounds, dachshunds, golden retrievers, German shepherds,
Manchester terriers, and Shetland sheepdogs. The condition has been
identified in more than 50 breeds of dogs.
Overview: Occurring because of abnormalities involving a
protein called von Willebrand's factor, von Willebrand's disease is
an inherited bleeding disorder of dogs. A large number of breeds can
be affected with the disease, but the breeds most commonly diagnosed
include Doberman pinschers, Scottish terriers, Shetland sheepdogs,
and Airedale terriers. Dogs with the illness will many times have no
symptoms at all, but when symptoms do occur, abnormal bleeding
results. Both spontaneous bleeding and excessive hemorrhage in
response to a stimulus such as trauma or routine surgery have been
observed.
Since the exact genetic manner in which the disease is transmitted
is often unknown, and since reliable tests to identify carriers of
the disorder are not always available, von Willebrand's disease is a
very difficult condition to eradicate. When excessive hemorrhage
occurs, it is best treated by careful use of physical techniques
that stop bleeding, such as suturing and cautery. The administration
of blood or blood components that help to replace deficient
concentrations of von Willebrand's factor will also be important. In
some animals, pre-treatment with a substance called DDAVP may allow
for temporary increases in von Willebrand's factor concentration
that will protect them during periods when they are at risk for
bleeding.
Clinical Signs: Many dogs with von Willebrand's disease never
have clinical signs. Others will bleed inappropriately during
surgeries, other stressful episodes, or when they are injured. Less
commonly, affected dogs will bleed spontaneously, often from the
nasal cavity or the urinary tract.
Symptoms:
See clinical signs.
Description: Von Willebrand's disease refers to a bleeding
disorder that results from reduced concentrations of a specific
protein called von Willebrand's factor. This substance plays a key
role in the adherence of platelets, the cells that normally help
blood clot, to collagen, a protein exposed by injury to blood
vessels. Dogs with von Willebrand's disease may bleed spontaneously,
most frequently from the nose, the mouth, and the urinary tract.
More frequently, affected dogs bleed only when there is a stimulus
for bleeding, such as an injury or surgery. Von Willebrand's disease
can be a frustrating condition to diagnose, manage, and prevent
because not all dogs with low concentrations of von Willebrand's
factor have symptoms related to the disease.
Von Willebrand's disease is often classified according to the type
and presence of different components of the von Willebrand's factor,
called multimers. In type I von Willebrand's disease, all the
different multimers are present, but in concentrations that are
below normal. This type is the most common form of the disease and
is characterized by bleeding from the mouth, nose, and urinary
tract. Although spontaneous bleeding may not occur, excessive
hemorrhage may be seen during elective procedures such as
dentistries, ear cropping or tail docking, spaying, and castration.
Breeds affected with Type I von Willebrand's disease include the
Doberman pinscher, Airedale, Shetland sheepdog, and Pembroke Welsh
corgi.
With type II von Willebrand's disease, smaller multimers are
present, and there is a lack of the larger multimers, which are more
important in the clotting process. This is a relatively uncommon
form of the disease, but can result in severe bleeding episodes.
German shorthaired pointers are most commonly affected.
Type III von Willebrand's disease is the most severe form. Animals
with this type of the illness lack any measurable von Willebrand's
factor and as a result, they can experience severe blood loss. The
breeds most commonly diagnosed with this form of the disease are
Scottish terriers and Chesapeake Bay retrievers.
Diagnosis: The easiest test for inappropriate bleeding due
to von Willebrand's disease is called the oral mucosal bleeding
test. This is performed by making a standardized incision on the
inside of the lip. This test is not specific for von Willebrand's
disease since other conditions can cause prolonged mucosal bleeding
times.
The most commonly used test that is more specific for the diagnosis
is the measurement of von Willebrand's factor antigen on a plasma
sample. Other diseases can cause this result to be artificially
increased, however
Prognosis: The prognosis for von Willebrand's disease
depends on whether signs of excessive hemorrhage are present, and
whether the hemorrhage is controlled before critical amounts of
blood are lost. For those dogs that are hemorrhaging but have no
access to blood or blood component therapy, the outlook can be very
grim
Transmission or Cause: The cause of von Willebrand's disease is
deficiency of a protein called von Willebrand factor. This substance
plays a key role in the adherence of platelets, the cells that
normally help blood clot, to collagen, a protein exposed by injury
to blood vessels. Von Willebrand factor may also play a role in the
adhesion of platelets to other platelets during blood clot
formation. Deficiencies in von Willebrand's factor are inherited.
Treatment: The primary treatment for von Willebrand's
disease is the administration of blood or blood products to patients
with active or anticipated bleeding episodes. A blood product called
cryoprecipitate contains large amounts of von Willebrand factor, but
it is seldom available. More commonly, the veterinarian will use
fresh plasma, or plasma that was frozen immediately after collection
and then thawed. Whole fresh blood may be used if hemorrhage has
been severe.
The administration of a drug called DDAVP may be helpful in
preventing hemorrhage in some affected animals if it is given prior
to the time that bleeding occurs. This drug increases levels of von
Willebrand factor available for the clotting process. DDAVP can also
be given to dogs donating blood prior to blood collection, so that
samples with high von Willebrand factor activity can be obtained.
Not all dogs respond to DDAVP
Prevention: Prevention of von Willebrand's disease is a very
difficult issue. Since the disease is hereditary, the ideal way to
eliminate it would be to avoid breeding affected dogs. However, not
all dogs with low von Willebrand's factor concentrations have
significant bleeding. The mere fact that the concentration is low
does not always mean that clinically significant problems will
occur, even in breeds in which a significantly high number of dogs
have reduced von Willebrand's factor. If all dogs that tested low
for the factor were eliminated from breeding, then breeding programs
would be quite restricted. Certainly, though, it makes sense not to
breed dogs that have had clinically significant episodes of bleeding
due to von Willebrand's disease, no matter what their breed.
In an affected dog, problems may be avoided prior to elective
surgeries by remembering to screen for this condition, especially if
previous bleeding episodes have occurred or if there is a familial
history of bleeding. Pre-treatment with DDAVP may help avert
disastrous consequences, as will having blood products on hand in
case they are needed.
