Acquired von Willebrand disease in patients with high platelet counts.

For patients with high platelet counts an inverse relationship has been established between platelet counts and large vWf multimers in plasma. Platelets are currently thought to be primarily involved in the pathogenesis of this decrease in plasma large vWf multimers, presumably by binding large vWf multimers, resulting in their effective removal from the circulation and/or by degrading (platelet-bound) vWf. In patients with myeloproliferative disorders associated with high platelet counts, a decrease in large vWf multimers in plasma may potentially compromise primary hemostasis. Patients with reactive thrombocytosis exhibit a similar reduction in large vWf multimers in plasma, but their clinical course is usually not complicated by bleeding, probably as a consequence of increased circulating vWf levels due to the behavior of vWf as a reactive protein, which compensates for the relatively decreased levels of large vWf multimers in plasma.