Ultrastructure of myeloma cells in a case with crystalcryoglobulinemia.

The bone marrow of a patient with multiple myeloma of the IgG2 Kappa type with spontaneously crystallizing cryoglobulin was studied by electron microscopy. The ultrastructure of the myeloma cells disclosed the presence of a crystalline material in the cytoplasm within the rough endoplasmic reticulum (RER) as well as in extracisternal sites. The crystalline material was also seen extracellulary with a distinctly unique subunit structure. The tubular units measured 200 +/- A (SEM) externally with an internal diameter of 100 +/- A (SEM). The intracellular distribution did not indicate a characteristic organelle association usually observed in protein synthesizing cells. It is suggested, based on the present observations and the findings of others, that the crystalline material may represent polymerized protein synthesized by free ribosomes mostly in extracisternal locations, a pattern often seen in neoplastic plasma cells. Diffusion to extracisternal sites of precrystalline material through the membranes of the RER is a possible alternative mechanism.