A 46-year-old man with homozygous β-thalassemia intermedia, extramedullary hematopoiesis, severe hemolytic transfusion reactions, and mild iron overload presented with unexplained progressive hypoproliferative anemia and rising serum creatinine. Serum protein electrophoresis and immunofixation studies identified an immunoglobulin G-λ monoclonal paraprotein of 1.6 g/dL. A bone marrow biopsy was performed. A peripheral blood smear (panel A: original magnification ×60, Wright-Giemsa stain) showed marked anisopoikilocytosis, microcytic hypochromic red cells, and numerous target cells. The bone marrow aspirate (panel B: original magnification ×40, Wright-Giemsa stain) showed marked erythroid hyperplasia (myeloid erythroid ratio, ∼1:7) and numerous admixed macrophages with small nuclei and abundant feathery/globular sea-blue cytoplasm (pseudo-Gaucher cells). The bone marrow biopsy was hypercellular for age (∼90% cellularity) with erythroid hyperplasia and macrophage aggregates with pale cytoplasm (panel C: original magnification ×20, hematoxylin and eosin stain [inset, original magnification ×100]). Plasma cells were increased, comprising ∼15% by CD138 (panel D: original magnification ×10, immunohistochemical stain) and were λ-restricted (panel E: original magnification ×20, immunohistochemical stain) consistent with a diagnosis of plasma cell myeloma.

Pseudo-Gaucher cells have been described in thalassemia, acute and chronic leukemias, lymphomas, and myeloma, and represent macrophages scavenging membrane glycolipids in the setting of high cell turnover. However, sheet-like proliferations of pseudo-Gaucher cells as seen here are unusual and may obscure neoplastic cells, posing a diagnostic challenge.