Blastic plasmacytoid dendritic cell neoplasm presenting as leukemia without cutaneous lesion.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic malignancy, recognized as a distinct entity in the WHO 2008 classification of hematolymphoid neoplasm. Described for the first time in 1994 as CD4+ cutaneous lymphoma with high expression of CD56, BPDCN has been known previously with various names such as blastic natural killer (NK) leukemia/lymphoma, agranular CD4+ CD56+ hematodermic neoplasm, and agranular CD4+ NK cell leukemia. This disease usually presents with cutaneous involvement as the first manifestation, with subsequent or simultaneous spread to bone marrow and peripheral blood. Leukemia as the first presenting symptom without any cutaneous involvement is a rare finding and can masquerade as acute undifferentiated leukemia. We present here such a case of a 59-year-old male who presented as leukemia without any cutaneous lesion but subsequently developed a scalp nodule.