Extracellular and intracellular crystal deposition in plasma cell myeloma.

A 68-year-old man presented with pain and malaise. Laboratory studies showed pancytopenia, hypercalcemia, increased creatinine, and proteinuria. Serum protein electrophoresis revealed an M-spike (0.2 g/dL) and immunofixation confirmed l-light chain. Bone marrow showed sheets of l-light chain restricted plasma cells with readily identifiable extracellular hexagonal crystals on aspirate and biopsy (panel A), and occasional intracellular crystals in plasma cells on biopsy (panel B). The crystals were eosinophilic by hematoxylin and eosin stain. They failed to stain for Wright-Giemsa or k-/l-light chains. No giant cell reaction was observed.