Blastic Plasmocytoid Dendritic Cell Neoplasm With Pseudo-Lymphoid Morphology Mimicking Lymphoid Malignancy

Abstract

A 60-year-old male presented with spontaneous hematomas and cervical adenopathy. Laboratory workup revealed hemoglobin 12.3 g/dL, platelet 56 × 10⁹/L, and leukocyte 14.7 × 10⁹/L. The automated cell counter (Sysmex XN) reported 9% neutrophils (1.32 × 10⁹/L) and 86% lymphocytes (12.6 × 10⁹/L), suggestive of a lymphoproliferative disorder. Blood smear showed atypical lymphoid cells with normal size, mature chromatin, and scant cytoplasm Figure 1 (Panel A), while numerous lysed cells were also observed (Panel B). About 10% of these cells displayed cytoplasmic vacuoles, occasionally coalescing, and 10% appeared larger with grayish cytoplasm (Panel C and D). Due to the apparent lymphocytosis, flow cytometry immunophenotyping was performed (Navios EX, Beckman-Coulter). Surprisingly, 62% of the leukocytes consisted of a CD45+low blastic population. These cells were negative for common lymphoid (CD19/CD20/CD22/CD24/cCD79a/CD3/CD5/CD8/CD10) and myeloid antigens (CD34/CD38/CD13/CD14/CD42b/CD61/CD64/CD65/CD117/cMPO), but were positive for CD4(weak)/CD56/CD123(strong)/HLA-DR(strong)/CD33 (Panel E and F). A cutaneous lesion was found on the patient's back, and bone marrow aspiration confirmed 82% of the same population with additional phenotypic markers indicative of pDC lineage (CD303+weak/CD304+/cTCL1+/BadLamp+), supporting the diagnosis of Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN). The neurological examination was normal, and cerebrospinal involvement was inconclusive due to hemorrhagic cerebrospinal fluid samples. Furthermore, the mutational profile performed on bone marrow aspirate was consistent with BPDCN, revealing mutations in TET2, ASXL1, and NF1, as well as a subclonal NRAS mutation and deletions in the IKZF1 and ETV6 loci.

BPDCN is a rare hematologic malignancy, with diverse morphological presentations. While the classic blastic morphology, often exhibiting “pearl necklace” cytoplasmic appearances and “hand-mirror-like” projections, is the most common presentation, this case displayed an unusual morphology dominated by pseudo-lymphoid cells. Although a subset of pseudo-lymphoid cells is commonly observed in BPDCN, this case was remarkable in that nearly all cells exhibited this distinctive morphology. Such atypical presentation can be deceptive, initially mimicking lymphoid malignancies. Here, the immunophenotypic profile was crucial in establishing the accurate diagnosis.

FIGURE 1

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(A) Blood smear review showing atypical lymphoid cells with normal size, mature chromatin, and scant cytoplasm, mimicking lymphoid malignancy, original magnification × 1000, May-Grünwald Giemsa stain. (B) Lysed cells on the blood smear review. (C) Blood smear review showing atypical lymphoid cells with cytoplasmic vacuoles, occasionally coalescing. (D) Blood smear review showing atypical lymphoid cells with larger and grayish cytoplasm. (E) Flow cytometry plot showing low CD4 positivity and CD56 positivity of the blast population. (F) Flow cytometry plot showing strong HLA-DR positivity and strong CD123 positivity of the blast population.