Proteinaceous lymphadenopathy due to monoclonal nonamyloid immunoglobulin deposit disease

We report two cases of lymph node enlargement due to massive extracellular nonamyloid immunoglobulin deposits that obscured the underlying cellular pathologic condition. In both cases, the deposits were demonstrated to be restricted to a single heavy and light chain, consistent with a monoclonal paraprotein, and cytoplasmic staining in the lymphocytes or plasma cells was identical to that of the paraprotein. The use of the protein A-gold technique was instrumental in revealing a monoclonal pattern in one case in which light microscopic immunohistochemistry did not reveal a clear-cut monoclonal pattern in the extracellular deposits. This case was subsequently shown to have multiple myeloma, while the second case has had an unusual history of hypocomplementemic vasculitis and normal bone marrow. Neither case had evidence of significant renal disease.