Non-secretory or low-secretory myeloma with intracellular kappa chains. Report of six cases and review of the literature.

This report concerns six cases of multiple myeloma characterized by either no demonstrable monoclonal immunoglobulin in plasma or urine or by trace amounts (less than or equal to 0.1 g/l) of monoclonal kappa chains in the urine. In all cases there was an infiltration of the bone marrow by plasma cells containing kappa chains but no heavy chains. A retrospective analysis was made of 126 consecutive cases of Bence Jones myeloma. The number of kappa and lambda cases was approximately the same. All cases secreting less than or equal to 0.1 g light chains per 1 urine were of kappa type. This contrasts with a kappa/lambda ratio of 1.4-1.9 among reported series of M-components containing both heavy and light chains. A review of reported cases of non-secretory myeloma revealed a preserved capacity for Ig synthesis in the majority of cases and among these a preponderance of kappa chain producing clones. These observations might be explained by a higher tendency for kappa chain producing cells to mutate to low secretors or to cells producing abnormal light chains which are catabolized rapidly. The clinical data from our patients do not indicate a more pessimistic prognosis in non- or low-secretory myeloma, than in other cases of multiple myeloma.