Hairy cell leukemia with marked lymphocytosis.

Abstract

Hairy cell leukemia (HCL) is a rare small B-cell lymphoproliferative disorder. The neoplastic cells have round to oval nuclei and abundant cytoplasm with “hairy” projections seen in the peripheral blood and bone marrow. They typically diffusely infiltrate bone marrow and spleen. Immunophenotypically, they strongly express CD103, CD22, CD11c, and CD25. Hairy cell leukemia commonly presents with pancytopenia and splenomegaly with few circulating neoplastic cells. We describe the case of a 42-year-old man who presented at our institution with marked leukocytosis (white blood cell count, 98 300/μL) and splenomegaly.The patient had no significant past medical history. His hemoglobin level was 9.9 g/dL and his platelet count was 154 000/μL. Review of a peripheral blood smear demonstrated marked lymphocytosis consisting of larger than usual lymphocytes with round to oval, eccentrically located nuclei; small inconspicuous nucleoli; and relatively abundant cytoplasm (Figure 1). Most of the lymphocytes displayed cytoplasmic projections (Figure 1, inset). Many of the cells were tartrate-resistant acid phosphatase (TRAP) positive (Figure 2). A normochromic, normocytic anemia with occasional ovalocytes and teardrop cells was also noted. The bone marrow core biopsy was markedly hypercellular (90%), with most of the medullary space occupied by small to medium-sized, monotonous-appearing lymphocytes with abundant cytoplasm (Figure 3). Flow cytometric analysis performed on the bone marrow aspirate demonstrated these cells to be κ-light chain restricted and CD19+, CD20+, CD5−, CD10−, CD11c+, CD103+, and CD25+.The differential diagnosis of the peripheral blood smear in this case would include HCL; chronic lymphocytic leukemia; prolymphocytic leukemia; the leukemic phase of mantle cell, follicular, and marginal zone lymphomas; and the rare Japanese variant of HCL (HCLV). The morphology, cytochemistry, and immunophenotype (CD19+, CD20+, CD11c+, and CD103+) of the neoplastic cells in our case are diagnostic for classic HCL, although the high lymphocyte count is a very unusual finding. The HCL variant, although extremely uncommon, does typically present with a marked lymphocytosis (usually around 50 000/μL). However, the neoplastic cells in HCLV typically have prominent nucleoli (resembling prolymphocytes) and are CD25− and CD103−. This was not the case in our patient.Cases of HCL with profound lymphocytosis have been reported only rarely in the literature. The highest white blood cell count reported was greater than 500 000/μL in a 49-year-old man who was treated with leukophoresis to bring his count to 20 000/μL.1 Although the case was reportedly TRAP positive, immunophenotyping was not performed. A 71-year-old man with classic HCL (CD22+, CD25+ by immunohistochemistry) reportedly had a white blood cell count as high as 323 000/μL. He eventually died as a result of leukostasis in the cerebral vasculature, which caused massive intracerebral hemorrhage.2 Golomb et al3 reviewed 71 cases of HCL and found that only 3 (4%) had white blood cell counts greater than 25 × 103/μL. Other authors have reported similar results; however, in most cases immunophenotyping was not performed.Our case represents another unusual case of HCL, with the diagnosis confirmed by morphology, immunophenotyping, and cytochemistry. Additionally, although the other cases cited were reportedly TRAP positive, our case may be the first reported in the literature with such a marked lymphocytosis (95 000/μL) that was shown to be CD11c+ and CD103+ (a relatively new and more specific antibody) by flow cytometry. Because positive TRAP staining is occasionally seen in other conditions, the question is raised as to whether some of the cases reported were truly cases of classic HCL. Moreover, this case as well as possibly the previous cases illustrate that although patients with classic HCL usually present with pancytopenia, rare cases can present with marked leukocytosis. This possibility should be kept in mind in order to provide accurate diagnosis and proper treatment of this disease. Our patient received a cycle of 2-chlorodeoxyadenosine (2-CdA) immediately following diagnosis. Three months later, circulating hairy cells were not seen on peripheral blood smear. Platelet and white blood cell counts normalized. A bone marrow biopsy performed at this time showed minimal residual disease (approximately 5% hairy cells), and flow cytometry detected a small CD11c+, CD25+, CD103+ population of hairy cells. Currently, the patient is doing well clinically.