Acquired von Willebrand's syndrome due to an inhibitor of IgG specific for von Willebrand's factor in polycythemia rubra vera

A patient with acquired von Willebrand's syndrome associated with polycythemia rubra vera is described. Ristocetin cofactor activity was decreased, while the levels of vWF:Ag and VIII:C were normal. Crossed immunoelectrophoretic analysis showed that vWF:Ag was composed of much more anodic component. The mixture study using pooled normal plasma and the patient IgG fractions showed the inhibition of ristocetin cofactor and the decrease of less anodic parts of vWF:Ag in normal plasma. After 1-deamino-8-arginine vasopressin (DDAVP) infusion the marked increases of vWF:Ag, VIII:C and ristocetin cofactor and a rapid return of ristocetin cofactor to the baseline were observed. Transient increase of vWF:Ag after DDAVP infusion showed less anodic forms and in the relative proportion as normal plasma. The present study showed that the patient IgG fractions had the specific inhibitory activity against the antigenic sites on the active subfractions of von Willebrand's factor.