A 71 year old man with a history of hypertension, glaucoma, and chronic kidney disease presented with gastrointestinal bleeding. A CT scan revealed a colonic mass and a right hemicolectomy was performed that showed multiple tubulovillous adenomas which harbored high grade dysplasia. Because of persistent anemia (hemoglobin: 7.3 g/dl) and thrombocytopenia (platelets 29,000/ul), a hematologic work-up was pursued. A bone marrow biopsy was performed and a diagnosis of plasma cell myeloma was rendered with the abnormal plasma cells representing 70-80% of total cells. Approximately 5 to 10% of the plasma cells contained Auer rod-like inclusions (figures 1, 2). Histiocytes with engulfed Auer rod-like inclusions were also present (figures 3, 4). The serum kappa to lambda ratio was 2061:1 and the urine free light chains were 75900 g/L. Karyotypic analysis showed loss of Y chromosome (45,X,-Y[5]/46,XY[15]) and FISH panel showed atypical CCND1/IGH rearrangements.

Plasma cells with Auer-rod like inclusions are rarely reported and are shown to be always associated with κ-light chain. Morphologically they resemble the Auer rods of myeloid cells; however they are composed of plasma cell enzymes such as acid phosphatase, α-N-esterase or β-glucuronidase rather than myeloperoxidase or chloroacetate esterase of myeloid cells. Prognosis of plasma cell myeloma with the presence of Auer rod-like inclusions is unclear.