A 62-year-old man presented with headache, dysarthria, and a right subdural hematoma. Laboratory studies were remarkable for leukocytosis (white blood cells, 29.4 × 109/L), thrombocytopenia (platelets, 87 × 109/L), and anemia (hemoglobin, 7.8 g/dL) without rouleaux. Many abnormal cells (48%) with Auer rod–like inclusions were noted on peripheral blood smear (panel A). Initial flow cytometric studies revealed a prominent population positive for CD45 (dim), CD38, HLA-DR, and CD13 (partial), and negative for CD34, CD117, MPO, CD33, CD19, TdT, and CD3 (surface and cytoplasmic). Additional immunophenotyping to evaluate the CD38+CD34−CD117−CD3−CD19− “blast” population demonstrated plasmacytic lineage with expression of CD138, CD56 (subset), and cytoplasmic kappa light chain restriction (panel B). Approximately 93% kappa-restricted plasma cells were noted on the subsequent bone marrow evaluation, with a complex karyotype including hyperdiploidy and TP53 deletion. Subsequent studies showed an immunoglobulin G kappa serum and urine monoclonal paraprotein that persisted despite bortezomib/lenalidomide therapy. Lytic lesions also developed several months later.
Greater than 20% circulating plasma cells characterize plasma cell leukemia, an aggressive variant of plasma cell myeloma. Auer rod–like inclusions have been described in plasma cell neoplasms; however, they may be mistaken for evidence of myeloid differentiation when occurring in the context of an acute leukemia-like presentation. Comprehensive immunophenotyping is instrumental for accurate diagnosis.
A 62-year-old man presented with headache, dysarthria, and a right subdural hematoma. Laboratory studies were remarkable for leukocytosis (white blood cells, 29.4 × 109/L), thrombocytopenia (platelets, 87 × 109/L), and anemia (hemoglobin, 7.8 g/dL) without rouleaux. Many abnormal cells (48%) with Auer rod–like inclusions were noted on peripheral blood smear (panel A). Initial flow cytometric studies revealed a prominent population positive for CD45 (dim), CD38, HLA-DR, and CD13 (partial), and negative for CD34, CD117, MPO, CD33, CD19, TdT, and CD3 (surface and cytoplasmic). Additional immunophenotyping to evaluate the CD38+CD34−CD117−CD3−CD19− “blast” population demonstrated plasmacytic lineage with expression of CD138, CD56 (subset), and cytoplasmic kappa light chain restriction (panel B). Approximately 93% kappa-restricted plasma cells were noted on the subsequent bone marrow evaluation, with a complex karyotype including hyperdiploidy and TP53 deletion. Subsequent studies showed an immunoglobulin G kappa serum and urine monoclonal paraprotein that persisted despite bortezomib/lenalidomide therapy. Lytic lesions also developed several months later.
Greater than 20% circulating plasma cells characterize plasma cell leukemia, an aggressive variant of plasma cell myeloma. Auer rod–like inclusions have been described in plasma cell neoplasms; however, they may be mistaken for evidence of myeloid differentiation when occurring in the context of an acute leukemia-like presentation. Comprehensive immunophenotyping is instrumental for accurate diagnosis.
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