The outcome of idiopathic Bence Jones proteinuria.

The authors studied two patients with idiopathic Bence Jones proteinuria (BJP) that fulfill all the criteria proposed by Kyle and Greipp. None had evidence of overt multiple myeloma, of its variants, of primary systemic amyloidosis, or of other lymphoid tumors. In a patient with kappa type idiopathic BJP an elevation of a labelling index was found when an evolving myeloma developed 2 years later. The other had benign lambda type BJP until he died of bronchogenic carcinoma after 14 years. In most of patients with idiopathic BJP overt multiple myeloma or systemic amyloidosis have developed after a long period. An elevation of labelling index in the course of illness is expected to be a premonitory sign for malignant transformation. Idiopathic BJP may be characterized by less nephrotoxicity or amyloidogenicity of Bence Jones protein synthesized as well as a slow growth rate of tumor cells.