Phagocytic plasma cells in a patient with smoldering myeloma

Abstract

A 43-year-old man, originally from Cuba, was referred in June 2012 because of a 6-month history of fatigue and weight loss. Physical examination was unremarkable. Laboratory findings revealed a IgG Lambda monoclonal protein level of 3.6 g/L serum IgG. Quantitative immunoglobulin determinations showed levels of IgG 14.8 g/L, IgA 1.4 g/L, and IgM 0.8 g/L. Lactate dehydrogenase (LDH) was slightly elevated at 284 U/L. Other biochemical data, including hemoglobin, reticulocyte count, platelet count, and leukocyte count, were within normal limits. Urine immunoelectrophoresis was negative for Bence Jones protein. Skeletal X-rays showed no lytic lesions. The bone marrow was normocellular, with normal maturing trilineage hematopoiesis. The aspirate showed 18 % infiltration of plasma cells, some of which contained several Russell bodies. Active phagocytosis, mainly of granulocytes, by plasma cells was a remarkable feature (Fig. 1). Immunophenotypic characterization of plasma cells showed expression of CD 38, CD 138, and CD56 antigens. The patient was diagnosed with smoldering myeloma. As recommended in the guidelines, the patient has been followed without starting chemotherapy. Under normal circumstances, plasma cells have no phagocytic function. Phagocytic plasma cells have been reported in association with lymphoproliferative disorders, and occasionally in patients with multiple myeloma. Phagocytosis by plasma cells in patients with smoldering myeloma is extremely rare and has only been described twice previously. In 1986 and 1987, two patients with asymptomatic multiple myeloma were described in which phagocytic plasma cells were present in the bone marrow. None of these reports provided an explanation for this phenomenon, and its clinical significance remains unknown. There have been speculations that the presence of CD15, a myeloid marker expressed on phagocytic myeloma cells, is associated with phagocytosis. There are other non-B cell antigens, such as CD56, that malignant plasma cells might rarely express. Normal plasma cells are typically CD56-negative. CD56 antigen is expressed in NK/T cell lymphoma, multiple myeloma, and AML. CD56 is a signaling receptor that impacts cellular adhesion, proliferation, differentiation, and apoptosis. Overexpression of CD56 in malignant neoplasms is associated with an aggressive tumor type, progression of multiple myeloma, and reduced overall survival in patients with AML and ALL. Jekarl et al. describe an association between CD56 antigen expression level and the percentage of hemophagocytosis in AML with t(16;21), but the mechanisms underlying this phenomenon remain unknown. A longitudinal retrospective study showed rapid progression to multiple myeloma in 85 % of CD56-positive MGUS patients. We speculate that the presence of CD56 antigen in our patient (Fig. 2) may not only be related to hemophagocytosis, but also lead to the rapid evolution of symptomatic multiple myeloma. The prognosis and time of progression to symptomatic multiple myeloma of patients with smoldering myeloma and phagocytic plasma cells are unknown. Further studies are needed to clarify the mechanisms leading to hemophagocytosis in plasma cells. T. Sayar Bahri (&) F. Weerkamp M. B. L. Leys Department of Internal Medicine, Maasstad Hospital, Rotterdam, The Netherlands e-mail: tanaz.bahri@gmail.com