Multiple myeloma with crystalline inclusions in most hemopoietic cells.

Intracytoplasmic inclusions were observed at light and electron microscopy in the cells of most of the hemopoietic series, including erythroblasts, in a case of multiple myeloma IgG kappa. The inclusions were of crystalline nature, surrounded by smooth membrane. An indirect immunoperoxidase method on thick sections confirmed their immunoglobulin G kappa nature. The fact that crystals were observed in various hemopoietic series suggests that, except for the plasma cells, their presence is more likely due to phagocytosis than to synthesis and, therefore, that they are not a clone marker.