Description

Von Willebrand disease (VWD) is an inherited bleeding disorder

of the platelets that occurs in dogs, cats, and people. Platelets are

responsible for helping blood clot. Von Willebrand factor is a protein

produced by platelets that helps platelets stick together and

form a clot. When this factor is abnormal or deficient, platelets do

not effectively stick together, and the result is prolonged or inappropriate

bleeding.

Causes

Three types of VWD exist, depending on the type and amount

of factor present. In type I, the factor is normal but is present in

very low amounts, and the severity of bleeding varies. Type I is

most common in the Doberman pinscher, German shepherd dog,

Shetland sheepdog, and standard poodle. In type II, the factor proteins

are abnormal and decreased, which results in more severe

bleeding episodes than in type I. Type II disease is typically seen

in German shorthaired and wirehaired pointers. In type III, the factor

is not made at all, and this is the most severe form. Type III is

most commonly identified in the Scottish terrier, Chesapeake Bay

retriever, and Shetland sheepdog.

Clinical Signs

Excessive or abnormal bleeding is the primary clinical sign of

VWD. Because this is an inherited condition, signs may be seen

early in life. Excessive bleeding from the gums occurs when baby

teeth fall out. Nose bleeds, blood in the urine, dark or tarry stools,

and swollen, painful joints may also occur. Sometimes excessive

bleeding is not noted until after trauma or during surgery. Events

that further affect platelet function, such as vaccination or use of

nonsteroidal anti-inflammatory medications, may cause temporary

bleeding and mild bruising.

Diagnostic Tests

In general, dogs with a suspected bleeding problem initially

undergo routine laboratory testing, which may include a complete

blood count, platelet count, biochemistry profile, and screening

coagulation tests. If VWD is suspected, a test may be done in the

clinic to assess platelet function; this is called the buccal mucosal.

This test is not specific for VWD, but an abnormal bleeding time

result increases suspicion for the disease.

To diagnose the presence of VWD, the amount of von

Willebrand factor in the blood must be measured. The results can

be labeled as normal, borderline, or abnormal. Dogs with abnormal

amounts are at risk for increased bleeding tendency. Borderline

results are sometimes rechecked, because the laboratory assay can

be affected by many factors. The usual test for VWD does not

identify the type (I, II, or III) present. If it is necessary to determine

the type, further specialized tests must be run.

Some studies have shown a relationship between low thyroid

hormone levels (hypothyroidism) and VWD, so your veterinarian

may recommend thyroid tests to ensure that this is not a complicating

factor.

Treatment Options

There is no cure for VWD. Treatment involves administration

of normal von Willebrand factor during episodes of bleeding or

when surgery is anticipated. Von Willebrand factor by itself cannot

be purchased, but blood products containing the factor (such

as plasma or cryoprecipitate) can be obtained from normal donors.

Transfusions of these blood products are given during times of

active bleeding and prior to surgery.

Injections of a drug called DDAVP (desmopressin acetate) may

temporarily increase blood levels of von Willebrand factor for a

few hours and is sometimes administered prior to surgery. There is

some controversy as to whether this medication is effective. Dogs

diagnosed with hypothyroidism are usually placed on a thyroid

supplement.

Follow-up Care

Because there is no cure, prevention is aimed at eliminating

affected dogs from the breeding pool. All dogs from breeds at

risk for this disease and dogs with a history of VWD in their

genetic line should be tested. Affected and carrier individuals

should not be bred. Breeds routinely tested include the Doberman

pinscher, golden retriever, Shetland sheepdog, Rottweiler,

schnauzers, German shepherd dog, standard poodle, Scottish terriers,

Pembroke Welsh corgi, German shorthaired and wirehaired

pointers, and others.

Prognosis

Without treatment, severely affected dogs may bleed to death

following injuries or surgeries not considered to be life- threatening.

Dogs with borderline levels of von Willebrand factor may have

increased bleeding tendencies that are not life-threatening but

must be managed proactively with measures such as limiting the

use of medications that affect platelet function, avoiding unnecessary

invasive surgeries, and giving transfusions or DDAVP before

planned surgeries.