Abstract

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare myeloid neoplasm that is derived from immature plasmacytoid dendritic cells. It commonly presents as single or multiple violaceous papules, plaques, or nodules mimicking bruises and it rapidly spreads to extracutaneous sites with a dismal prognosis. Biopsy shows a dense dermal and subcutaneous infiltrate of blastic cells that are typically CD4+, CD56+, CD123+, TCL1+ and EBV-. We report an 85-year-old man with a history of metastatic bladder and prostate cancer being treated with chemoimmunotherapy who presented with an ulcerated plaque on his right upper arm of 3-4 months duration. Skin biopsy showed an ulcer with underlying dermal necrosis and large lymphoid cells, many resembling Hodgkin/Reed-Sternberg (HRS)-like cells. These HRS-like cells were PAX5+, EBV+, and CD30+, and they were associated with numerous CD4+ T-cells that were also CD10+, ICOS+ and BCL6+. Gene rearrangement studies demonstrated both a clonal B-cell population and a clonal T-cell population, and the case was submitted with a preliminary diagnosis of angioimmunoblastic T-cell lymphoma. However, there was a second, distinct proliferation of atypical blastic cells on one edge of the biopsy that were CD4+ and CD7+, but CD3-/CD2-/CD5-. These cells were CD56+, CD123+, TCL1+ and lysozyme-. A repeat biopsy of the lesion revealed sheets of blastic cells with the same immunophenotype and without evidence of ulceration or atypical HRS-like cells. This case demonstrates an unusual association between BPDCN and an EBV+ lymphoproliferative disorder compatible with EBV+ mucocutaneous ulcer. It highlights the challenges that dermatopathologists face in diagnosing cutaneous lymphoproliferative disorders, as biopsies are often small and more than one diagnosis may rarely be present in a single lesion.

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