Track

Case Reports

Abstract

Mature plasmacytoid dendritic cell proliferation (MPDCP) associated with myeloid neoplasm is characterized by clonal expansion of mature plasmacytoid dendritic cells in the skin, bone marrow, and rarely in the lymph nodes. MPDCP is described mostly in association with chronic myelomonocytic leukemia (CMML) but also acute myeloid leukemia and myelodysplastic syndrome. We report a rare case of a 75-year-old male with CMML who presented with violaceous papules on the chest, back, and arms. Biopsy revealed an interface and prominent periadnexal lymphocytic infiltrate. Most mononuclear cells were medium-sized, had eccentrically located round to oval nuclei with clumped chromatin, and did not look atypical. Most of them were CD4 and CD123 positive. A relatively small fraction was CD3 positive with no loss of expression of CD5 or CD7. TdT and CD56 were negative, while some cells expressed CD68 (PG-M1) and Granzyme B. Ki-67 immunostain showed a low proliferation index. These features favored the diagnosis of MPDCP over blastic plasmacytoid dendritic cell neoplasm (BPDCN). Hematological workup showed peripheral blood monocytosis, anemia, and thrombocytopenia. Bone marrow biopsy revealed a slightly increased blast count of 4% compared to no blasts seen nine months prior. Next-generation sequencing identified mutations in KRAS, NRAS, RUNX1, SRSF2, and TET2 genes. RAS pathway and TET2 gene mutations are seen at a higher frequency in patients with CMML and MPDCP. Increased awareness of this rare condition is crucial to prevent potential misdiagnosis, particularly as BPDCN, which shows overlapping features. Timely recognition by promptly investigating associated hematological conditions has important therapeutic implications.