#00064028

A 50-year-old male presented with a mid-thoracic compression fracture, osteoporosis of the lumbar spine (T-score of -3.9 on DEXA scan), hypercalcemia (11.4 mg/dL), anemia (Hgb 11.4 g/dL), and elevated total protein levels (9 g/dL). Flow cytometric analysis showing side scatter versus CD45 identified a population of CD45 dim positive cells (A). Of this population, the cells denoted in purple are CD34 negative compared to the CD34 positive green population (B), where the green population represents myeloid precursors, and the purple represents plasma cells. In the CD117 versus CD56 dot plot, both populations are positive for CD117 and CD56 (C). In the CD13 versus CD33 plot, the atypical plasma cells are positive for CD33 but negative for CD13, while the myeloblasts are positive for both markers (D). The dot plot of CD38 versus CD138 identifies CD38+/CD138+ plasma cells, indicated in purple (E). These plasma cells are positive for cytoplasmic Kappa chain (F). A bone marrow biopsy revealed diffuse infiltration by atypical plasma cells with eccentric nuclei, as shown by hematoxylin and eosin stain (G) and immunohistochemistry positive for CD138 (H). As demonstrated, CD33+/CD56+/CD117dim+ atypical plasma cells can closely mimic myeloblasts phenotypically, so flow cytometric results should be interpreted with caution. Overall, these clinical and histopathological findings are consistent with a diagnosis of multiple myeloma aberrantly expressing CD33, CD56, and CD117.