[An unusual case of multiple myeloma diagnosed by a noticeable decrease in the serum M-component level].

Abstract

The author has recently observed an unusual case of multiple myeloma, which was diagnosed by a noticeable decrease in the serum monoclonal IgG (kappa) level in close association with Bence Jones escape. [Case Report] In June 1986, a 61-year-old woman was noticed to have monoclonal gammopathy of undetermined significance (MGUS) at a local hospital. Bence Jones escape was found in association with a decrease in the serum M-component level in April 1991, when a diagnosis of indolent multiple myeloma was made. In April 1993, the daily amount of Bence Jones proteins excreted in the urine was 1 g. Examination of bone marrow aspirate demonstrated immature plasma cells in clusters. The patient was diagnosed of having overt multiple myeloma. The double immunofluorescence studies on the bone marrow plasma cells were performed. Only 40 percent of cells producing kappa light chains were found to be positive for gamma heavy chains, while all of gamma heavy chain-positive cells contained kappa light chains. kappa light chain-positive cells were stained neither with anti-alpha, nor with anti-mu. From the above-mentioned data, the proportion was about two cells producing IgG (kappa) to three cells producing kappa light chain alone. Thus, myeloma cells contained two morphologically identical but immunologically diverse subpopulations. Conceivably, the subclone producing kappa light chain alone could be derived from the original clone producing monoclonal IgG (kappa). Bence Jones escape of this type has not hitherto been described.