Ultrastructural features of the plasma cells in "non-secretory" myeloma

A case of "non-secretory" multiple myeloma is described. The diagnosis was based on the clinical picture, typical radiological findings, and infiltration of the bone marrow by myeloma cells which showed specific immunofluorescence staining mainly with antisera for IgM and kappa light chains. An attempt is made to explain the absence of pathological proteins in the serum, based on the ultrastructural findings of the myeloma cells, which showed "buddings" of the cell membranes containing endoplasmic reticulum and cytoplasmic material. It is suggested that the cells of the "non-secretory" type of multiple myeloma possess a normal excretory mechanism, but the pathological proteins are prevented to be secreted in the serum being surrounded by portions of the cell membrane.