tailieunhanh - Chapter 109. Disorders of Platelets and Vessel Wall (Part 9)

von Willebrand Disease vWD is the most common inherited bleeding disorder. Estimates from laboratory data suggest a prevalence of approximately 1%, but data based on symptomatic individuals suggest that it is closer to of the population. vWF serves two roles: (1) as the major adhesion molecule that tethers the platelet to the exposed subendothelium; and (2) as the binding protein for FVIII, resulting in significant prolongation of the FVIII half-life in circulation. The platelet-adhesive function of vWF is critically dependent on the presence of large vWF multimers, while FVIII binding is not. Most of the symptoms of vWD. | Chapter 109. Disorders of Platelets and Vessel Wall Part 9 von Willebrand Disease vWD is the most common inherited bleeding disorder. Estimates from laboratory data suggest a prevalence of approximately 1 but data based on symptomatic individuals suggest that it is closer to of the population. vWF serves two roles 1 as the major adhesion molecule that tethers the platelet to the exposed subendothelium and 2 as the binding protein for FVIII resulting in significant prolongation of the FVIII half-life in circulation. The platelet-adhesive function of vWF is critically dependent on the presence of large vWF multimers while FVIII binding is not. Most of the symptoms of vWD are platelet-like except in more severe vWD when the FVIII is low enough to produce symptoms similar to those found in Factor VIII deficiency hemophilia A . vWD has been classified into three major types with four subtypes of type 2 Table 109-2 . By far the most common type of vWD is type 1 disease with a parallel decrease in vWF protein vWF function and FVIII levels accounting for at least 80 of cases. Patients have predominantly mucosal bleeding symptoms although postoperative bleeding can also be seen. Bleeding symptoms are very uncommon in infancy and usually manifest later in childhood with excessive bruising and epistaxis. Since these symptoms occur commonly in childhood the clinician should particularly note bruising at sites unlikely to be traumatized and or prolonged epistaxis requiring medical attention. Menorrhagia is a common manifestation of vWD. Menstrual bleeding resulting in anemia should warrant an evaluation for vWD and if negative functional platelet disorders. Frequently mild type 1 vWD first manifests with dental extractions particularly wisdom tooth extraction or tonsillectomy. Table 109-2 Laboratory Diagnosis of von Willebrand Disease Type aPTT vWF Antigen vWF Activity FVIII Activity Multimer 1 Nl or uP down down down Normal distribution decreased in quantity 2A Nl or uP .