Evolution of ristocetin cofactor activity (VWF:RCo) and Willebrand factor antigen (VWF:Ag) and serum monoclonal immunoglobulin M (IgM) concentration over time in 4 patients with acquired von Willebrand syndrome. The solid line indicates the evolution of serum IgM concentration, the dashed line indicates VWF:Ag, and the line of alternating dashes and dots indicates the VWF:RCo. Arrows indicate that plasma exchanges have been performed. (A) Patient 296, (B) patient 314, (C) patient 333, and (D) patient 351.