Abstract

Proliferations of plasmacytoid dendritic cells (pDCs) are subclassified into two types: Blastic plasmacytoid dendritic cell neoplasm (BPDCN) and mature plasmacytoid dendritic cell proliferation (MPDCP). Neoplastic expansions of reactive pDCs cells are associated with myeloid neoplasia.

We describe the case of a 62 year-old-female who presented to the emergency department with numerous hemorrhagic nodules and papules on the face and extensor surfaces near the elbows, and neutropenic fever. The patient had a history notable for lupus erythematosus. A punch biopsy was performed which showed a robust dermal infiltrate of atypical intermediate-sized mononuclear cells. The infiltrate was positive for CD4, CD43, and CD123. CD3 and CD8 highlighted background T-cells. The infiltrate was negative for CD10, CD34, CD56, CD68, CD117, myeloperoxidase, lysozyme, TdT, and TCL-1. A concurrent lymph node biopsy revealed a similar proliferation wherein the mononuclear cells expressed CD4, CD123 and CD56. The findings favored a diagnosis of cutaneous and nodal involvement by a plasmacytoid dendritic cell proliferation. Given the association with myeloid neoplasia, a bone marrow biopsy was recommended which revealed previously unsuspected Acute Myelomonocytic Leukemia.

Plasmacytoid dendritic cell neoplasms can present as skin lesions or lymphadenopathy, both of which are associated with myeloid neoplasia. Awareness of this association may help prevent potential misdiagnosis of pDC proliferations as BPDCN and prompt investigation of possible myeloid neoplasms.