Systemic amyloidosis with a mesenteric mass which had the appearance of proteinaceous lymphadenopathy.

An autopsy case of systemic amyloidosis in a 46-year-old Japanese female who had M component in sera but no manifestations of myeloma is described. Autopsy revealed massive milky ascites and a large mesenteric mass, which showed histologically perivascular concentric deposition of eosinophilic materials with mixture of residual follicles and scattered plasma cells. These morphological findings closely resembled those seen in proteinaceous lymphadenopathy, and the material in the mesenteric mass proved to be an amyloid A lambda protein. Subsequent immunohistochemical observations strongly suggested that this mass lesion was a "burnt-out" plasmacytic dyscrasia.