Bence Jones protein in primary systemic amyloidosis.

The recent population-based study by Kyle et al,’ which was the first to provide precise epidemiologic information about primary systemic amyloidosis, reported the demonstration of a monoclonal (M)protein in the serum or urine from 16 of 21 patients (76%) with amyloid of unequivocal Ig origin (AL). However, the number of patients in whom free monoclonal Ig light chain (ie, Bence Jones [BJ] protein) represented the sole detectable M-protein was apparently lower than I would have expected to find in this disease. The frequency with which BJ proteinuria occurred in association with an intact M-protein in the serum is somewhat difficult to evaluate from the separate presentation of the results of the serum and urine investigations. All but one patient had the serum protein pattern analyzed by at least electrophoresis, with an M-protein band being recognizable in 18 (90%), whereas in only 2 (12%) of the 17 patients who had their serum further investigated by immunoelectrophoresis or immunofixation did the M-protein consist of free X light chain. The search for BJ protein by immunoelectrophoresis or immunofixation was negative in the urine from one-third of the 15 patients and 3 others had a normal urine electrophoretic pattern. Thus, negative results were obtained in 44% of the 18 patients who had their urine studied by at least electrophoresis. These figures most likely reflect the necessary inclusion in such a retrospective study of patients who had their serum and urine examined by using less sensitive techniques than those available at present. The same reason might also account in part for the 11% to 14% frequency of “nonsecretory” AL reported in other large series:“ from which the occurrence of BJ protein alone can be inferred to be as much as 43%.334 Over a 10-year period since 1980, when our laboratory introduced immunofixation in combination with a high-resolution agarose gel electrophoresisS for the routine investigation of M-proteins in the serum and concentrated urine, 18 patients (9 males and 9 females from 47 to 79 years of age; median, 68 years) were recognized as having systemic deposition of AL without evidence of coexistent