Von Willebrand syndrome
Von Willebrand syndrome is a deficiency or dysfunction of von Willebrand factor (vWF), a protein with binding sites for platelets, collagen, and factor VIII that “serves as a bridge between platelets and injury sites in vessel walls” and “protects factor VIII from rapid proteolytic degradation,” Dr. Hertweck said. Von Willebrand syndrome is the most common inherited congenital bleeding disorder. Although acquired von Willebrand syndrome is rare, it has grown in incidence among those with complex cardiovascular, hematologic, or immunologic disorders.
“Correct diagnosis is complex and not always straightforward,” Dr. Hertweck said, but “a positive response to questions in four categories is highly sensitive.” They are as follows:
• Menses lasting at least 7 days and interfering with a person’s daily activities.
• “History of treatment for anemia.
• Family history of a diagnosed bleeding disorder.
• History of excessive bleeding after tooth extraction, delivery, miscarriage, or surgery.
Diagnostic assays include platelet concentration of vWF antigen, an activity test of vWF-platelet binding, and factor VIII activity. However, you often need to repeat diagnostic testing because vWF antigens vary according to race, blood type, age, acute phase response, and menstrual cycle timing, Dr. Hertweck said.
“Remember to draw von Willebrand testing only during the first 3 days of the menstrual cycle when estrogen levels are at the nadir,” she said.
Because estrogen increases vWF, treatment for von Willebrand syndrome should be progestin only, either oral pills, medroxyprogesterone acetate (MPA, or Depo-Provera injections), or an etonogestrel implant.
Dr. Hertweck presented several cases of abnormal menstruation and extreme conditions such as severe menorrhagia. Outside of von Willebrand in such patients, possible platelet disorders could include Glanzmann thrombasthenia (a platelet function disorder that is caused by an abnormality in the genes for glycoproteins IIb/IIIa) and platelet storage pool disorder, both of which should be diagnosed by a hematologist.
Dr. Hertweck reported having a research grant from Merck related to contraceptive implants in adolescents.