VWF and histiocytic sarcoma: The binding of vWF to platelets in the presence of ristocetin as an agglutinating agent was reduced, while the analysis of vWF multimers using a semiautomatic Hydrasys 2 device (Sebia, Lisses, France, Fig. 2) and densitometric evaluation demonstrated a reduced distribution of high molecular weight vWF multimers, which indicated acquired von Willebrand syndrome, fulfilling the criteria for the diagnosis of HS (Fig. 2).[4]