Multiple myeloma, IgA kappa type, accompanying crystal-storing histiocytosis and amyloidosis

An autopsy case of multiple myeloma, IgA kappa type, accompanying systemic crystal-storing histiocytosis and generalized amyloidosis, is reported. Besides multiple destructive lesions in the skeletal bones, nodular myeloma cell infiltrates were scattered in the liver, spleen, and both kidneys. Not only in these lesions but also in the reticuloendothelial organs, crystal-storing macrophages appeared dispersively or in clusters. Electron microscopically, numerous crystalline inclusions contained in the cytoplasm of macrophages were membrane-bound and of variable configuration, comprising of a homogeneous electron-lucid material. Enzyme cytochemically, almost all of the inclusions showed acid phosphatase activity. On the basis of the results obtained from the immunohistochemical, immunofluorescent and immunoelectron microscopic studies, it was considered that the crystalline inclusions stored in the macrophages were derived from IgA kappa immunoglobulin secreted from the myeloma cells and were formed within secondary lysosomes by crystallization during lysosomal digestion and degradation of the ingested immunoglobulin by macrophages. Generalized amyloidosis developed in different sites from those of the crystal-storing histiocytosis and were proven immunohistochemically to belong to AL amyloidosis probably derived from a certain group of A kappa precursor protein.