Abnormalities of von Willebrand factor in myeloproliferative disease: a relationship with bleeding diathesis

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Abstract
We studied factor VIII related properties in 24 patients with increased platelet number. Twenty‐one were affected by myeloproliferative disorders (eight had polycythaemia vera, 13 had essential thrombocythaemia) and three had secondary thrombocytosis. Normal levels of VIII: C and VIIIR: Ag were found while a significant (P<0.05) decrease of VIIIR:RCOF (43 ± 13%) related to a lack of larger multimers of VWF (39 ± 12%) was observed in 57% of patients with myeloproliferative disorders. A normal VWF pattern was found in the three patients with secondary thrombocytosis. The highest incidence of VWF abnormalities occurred in patients with essential thrombocythaemia (70%) in comparison with polycythaemic patients (38%). A significant (P<0.03) correlation between platelet count and the values of both VIIIR: RCOF and VWF multimeric pattern was observed only in patients with polycythaemia vera. The lowest levels of VIIIR: RCOF and the greatest loss of larger VWF multimers (less than 30%) were observed in two patients who presented bleeding symptoms at the time of study and a prolonged bleeding time. In addition, the relationship between VWF pattern and bleeding diathesis was supported by the fact that 75% of the patients with VWF abnormalities had bleeding history.