Abstract
An 82-year-old man with a low-grade malignant non-Hodgkin lymphoma and an IgG3 lambda monoclonal gammopathy presented a recently acquired bleeding tendency, characterized by recurrent epistaxis, easy bruising, and episodes of melena, requiring packed red blood cell transfusions. Coagulation studies showed a von Willebrand factor (vWF) defect (Ivy bleeding time, > 15 minutes; vWF antigen [vWF:Ag], 0.08 U/mL; ristocetin cofactor activity [vWF:RCoF], < 0.05 U/mL; collagen binding activity [vWF:CBA], 0.01 U/mL; absence of the high molecular weight multimers of vWF on multimeric analysis). Mixing experiments suggested the presence of an inhibitor directed against the vWF:CBA activity of vWF without significantly inhibiting the FVIII:C, vWF:Ag, and vWF:RCoF activities. The inhibitor was identified as an antibody of the IgM class by immunoabsorption of vWF and inhibitor-vWF complexes from the plasma of the patient. Subsequent immunoprecipitation experiments using recombinant fragments of vWF showed that the inhibitor reacted with both the glycoprotein Ib binding domain (amino acids [aa] 422–826) and the A3 (aa 909–1112) domain of vWF, but not with the A2 (aa 716–908) or D4 (aa 1183–1535) domains. We conclude that the IgM autoantibody inhibits the vWF:CBA activity by reacting with an epitope present on both the glycoprotein Ib and A3 domains of vWF.
Acquired von Willebrand disease caused by an autoantibody selectively inhibiting the binding of von Willebrand factor to collagen
