Hairy Cell Leukemia with Marrow Reactive Plasmacytosis and Mast Cell Hyperplasia: A Case Report and Brief Review of the Literature

Hairy cell leukemia (HCL) and HCL-like disorders, including HCL-variant, are disorders of heterogeneous mature lymphoid B-cells known for their hairy cell infiltration accompanied by a specific genetic profile, various clinical presentations, and, as they are uncommon hematological malignancies characterized by pancytopenia, the need for appropriate therapy. Sometimes HCL creates diagnostic challenges for clinicians, and its coincidence or association with mast cell and plasma cell infiltration is a rare condition. Herein, we report a case of HCL with confusing manifestations. A 44-year-old man was referred to the hospital for weakness, fatigue, and watery, non-bloody diarrhea. The laboratory tests showed pancytopenia, leading to a referral for bone marrow aspiration and biopsy. Medium to large cells exhibiting widespread cytoplasm, oval nuclei similar to monocyte nuclei (kidney-shaped) accompanied by an increased number of mast cells, and plasma cells were observed in the biopsy sample. In flow cytometry, the neoplastic cells were positive for CD19, FMC7, and the co-expression of the CD20/CD25, CD11C/CD22, and CD103 markers. In immunohistochemical staining, the mast cells were positive for CD117, the plasma cells were positive for CD138, and the hairy cells were positive for CD20. Overall, hematopathologists must be aware of various morphologic confounding factors such as lack of typical cell morphological features and increased plasma cell and mast cell infiltration in the diagnosis of patients with HCL.