A 3-day-old boy with a known family history of von Willebrand disease (VWD) type 2B was found to have marked thrombocytopenia on automated blood count (platelet count 7 × 109/L). Examination of the peripheral blood showed numerous aggregates of large well-granulated platelets (panel A; original magnification ×20, Wright-Giemsa stain), with few platelets noted outside of these collections (panel B; original magnification ×20, Wright-Giemsa stain). Red blood cell and white blood cell morphology was unremarkable. On the basis of a known family history and characteristic peripheral blood findings, a presumptive diagnosis of VWD type 2B was made.
VWD is the most common inherited bleeding disorder and is classified on the basis of the type of abnormality present in von Willebrand factor (VWF). VWD type 2B accounts for approximately 5% of cases and arises from various mutations in the VWF gene that increase the affinity of VWF for platelet glycoprotein Ib. The mutant VWF aggregates more readily with platelets, resulting in the loss of large VWF multimers from circulation and thrombocytopenia secondary to platelet sequestration or destruction. This is the only type of VWD recognized to cause thrombocytopenia (not including pseudo-VWD, a similar disorder of platelets), which is often intermittent and is dependent on circulating levels of high molecular weight multimers of VWF, which may be increased in the neonatal period.
