Double Bence Jones proteinuria

We have recently observed an unusual case of multiple myeloma with double Bence Jones proteinuria. Immunofixation clearly demonstrated monoclonal light chains of both kappa and lambda type in the urine. By double immunofluorescence staining, 11% of myeloma cells were found to be double producers. The marginal portion of cytoplasmic Russell bodies was stained with anti-lambda, while the core was diffusely stained with anti-kappa. Our results indicated that cells of common clonal origin produced Bence Jones proteins of both kappa and lambda type. No reference is found in the literature to such a finding in double Bence Jones proteinuria. In this article, in addition to the summary of nine cases of double Bence Jones proteinuria, possible explanations for this rare phenomenon are described to give a better understanding of this entity.