VON WILLEBRAND’S DISEASE
Von Willebrand’s disease, a common bleeding disorder affecting males and females equally, is usually inherited as a dominant trait. The disease is caused by a deficiency of von Willebrand factor (vWF), which is necessary for factor VIII activity. vWF is also necessary for platelet adhesion at the site of vascular injury. Although synthesis of factor VIII is normal, its half-life is shortened; there-fore, factor VIII levels commonly are mildly low (15% to 50% of normal).
Patients commonly have nosebleeds, excessively heavy menses, bleeding from cuts, and postoperative bleeding, although they do not suffer from massive soft tissue or joint hemorrhages. As the laboratory values fluctuate, so does the bleeding. For example, a careful history of prior bleeding may show little problem with postoperative bleeding on one occasion but significant bleeding from a dental extraction at another time.
Laboratory test results show a normal platelet count but pro-longed bleeding time and slightly prolonged PTT. These defects are not static, and laboratory test results can vary widely within the same patient over time.
Both the factor deficiency and the platelet impairment can be cor-rected by administration of cryoprecipitate, which contains factor VIII, fibrinogen, and factor XIII (or fresh frozen plasma, if cryo-precipitate is unavailable). Replacement continues for several days to ensure correction of the factor VIII deficiency; up to 7 to 10 days of treatment may be necessary after major surgery. Desmo-pressin (DDAVP), a synthetic vasopressin analog, can be used to prevent bleeding associated with dental or surgical procedures or to manage mild bleeding after surgery. Desmopressin provides a transient increase in factor VIII coagulant activity and may also correct the bleeding time. It can be administered as an intravenous infusion or intranasally. With major surgery or invasive proce-dures, both desmopressin and cryoprecipitate may be needed to prevent hemorrhage.