MM-218 Plasma Cell Myeloma-Associated Crystal-Storing Histiocytosis

Abstract

This study reports a plasma cell myeloma case, which presented with cytoplastic crystalline inclusions both in plasma myeloma cells and histiocytes in the bone marrow smears. A 39-year-old man with a history of chronic kidney disease (uremic stage) has been treated with regular dialysis in the past 6 years. He recently presented with anemia (hemoglobin, 99 g/L), and laboratory studies showed an IgA kappa paraprotein (30.5 g/L). Wright-stained bone marrow aspirate smears detected two types of cells containing globular, azurophilic, crystalline inclusions in the cytoplasm; one was relatively small in size with round eccentric nuclei, condensed chromatin, and scattered cytoplasmic crystals, consistent with plasma cells. Another was much larger in size with an irregular contour and abundant cytoplasmic crystals, consistent with histiocytes. The bone marrow biopsy showed 30% abnormal plasma cells associated with prominent proliferation of histiocytes. By immunohistochemistry, plasma cells were highlighted by CD138 and histiocytes were highlighted by CD68, corresponding to the two populations detected on smears. Plasma cells and histiocytes were both positive for K light chain by immunostain, which demonstrated that they contained the same immunoglobin deposition. The presence of immunoglobin crystals in plasma cells or histiocytes has been reported, but the detection of immunoglobin crystals in plasma cells and histiocytes simultaneously, as described in this case, is extremely rare. The pathogenesis of the clinical presence should be further studied.