Novel Ultrastructural Findings of Blastic Plasmacytoid Dendritic Cell Neoplasm.

A 64-year-old man presented with a 2-year history of cutaneous lesions on his face, trunk, left arm, and right leg. Physical examination revealed erythematous patches on his forehead, right ear, cheeks, lower jaw, right forearm, left lower thigh, and trunk [Figure 1a]. Superficial lymph nodes were not palpable. He was otherwise healthy and was taking no medication. Peripheral blood showed white blood cells of 1.6 × 103/μL, red blood cells of 3.46 × 106/μL, hemoglobin of 11.0 g/dL, and platelet count of 19 × 103/μL. The differential count showed 62% lymphocytes, 34% neutrophils, and 4% monocytes without atypical blood cells. Blood chemistry values were within normal ranges. A skin biopsy from the lower jaw revealed a diffuse sheet of small to medium-sized tumor cells with poor cytoplasm throughout the dermis and with the minimal involvement of the overlying epidermis [Figure 1b]. These cells were positive for CD4 [Figure 1c], CD56 [Figure 1d], CD123, and terminal deoxynucleotidyl transferase (TdT) but negative for cytoplasmic CD3, CD8, CD20, CD34, CD1a, and c-kit [Figure 1e]. Monoclonal T-cell receptor and immunoglobulin gene rearrangements were not detected. Flow cytometric analysis of the skin lesion revealed that CD4+and CD123+tumor cells accounted for 32.9% of the CD45-positive cells in the skin. However, the majority of the cells were negative for CD303 [Figure 1f]. A mild increase in mast cells presenting as evenly distributed scattered cells was seen among tumor cells in toluidine blue-stained sections. Transmission electron microscopy (TEM) showed that the tumor cells had microvillous processes on the cell surface. The nucleus had a prominent nucleolus and a moderate amount of heterochromatin. Intriguingly, the tumor cells were composed of mature dendritic cells [Figure 1g]. There were many rough endoplasmic reticulum and transport vesicles in the mature dendritic cell neoplasm. Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) demonstrated multiple foci of increased uptake in the skin, spleen, lymph nodes, and bone marrow. Based on these findings, the skin lesion was diagnosed as blastic plasmacytoid dendritic cell neoplasm (BPDCN) associated with multiple organ involvement. The patient was treated with 2 cycles of hyper CVAD/MA chemotherapy (cyclophosphamide, vincristine, doxorubicin, dexamethasone, methotrexate, and cytarabine). The treatment resulted in partial response, and his skin lesions markedly improved over the next month. Thereafter, the patient was followed-up for 16 months without the recurrence.

Figure 1

(a) There was invasive erythematous plaque in the right ear and right cheek. (b) A skin biopsy from the lower jaw revealed diffuse sheets of small cytoplasmic cells with poor cytoplasm throughout the dermis and with minimal involvement of the overlying epidermis (H&E, 10 ×). (c) Atypical cells expressed CD4 (40 ×). (d) Atypical cells expressed CD56 (40 ×). (e) c-kit-negative atypical cells (40 ×) (f) Flow cytometry analysis of the tumor. (g) Transmission electron microscopy (TEM) showed mature plasmacytoid dendritic cells

BPDCN is a rare aggressive lymphoma initially identified as the leukemic counterpart of plasmacytoid dendritic cells.[12] There is no description of skin BPDCN with regard to TEM findings and maturity status. It has been reported that BPDCN can be categorized into three maturational stages by CD34 and c-kit stainings.[3] Based on our findings, our case is a c-kit and CD34-double-negative mature immunophenotype. In previous studies in which TEM of bone marrow BPDCN was performed, CD34 and c-kit immunostainings were not performed, and thus the maturation stage was not clarified.[45] Although those cases showed a rough endoplasmic reticulum, our case also showed transport vesicles, which support the mature phenotype of BPDCN. In conclusion, the combination of immunohistochemical and ultrastructural analyses enables a more accurate diagnosis of this clinically heterogeneous tumor to be made.

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