Nonsecretory Myeloma

Patients with nonsecretory myeloma have no M protein in either the serum or urine with immunofixa-tion. This finding occurs in 1-5% of all patients with multiple myeloma.42 71-74 In 1027 patients with newly diagnosed myeloma, we found no M protein in the serum and urine with immunofixation in 29 (2.8%).42 Immunoperoxidase and immunofluorescence studies on plasma cells should be performed in all patients with nonsecretory myeloma. A cytoplasmic M protein is identified in about 85% of patients; no M protein can be found in the remaining, and these patients are considered to have "nonproducer" nonsecretory myeloma.75-78

Ultrastructural study of plasma cells shows the typical features observed in plasma cells of patients who have an M protein in the serum and urine.79 80 In contrast, in some cases of nonproducer or truly nonsecre-tory myeloma, ultrastructural studies show highly undifferentiated plasma cells.7781 The lack of M protein in the serum and urine of patients with nonsecre-tory myeloma may be from (1) the inability of plasma cells to excrete the immunoglobulin, (2) the low synthetic capacity of immunoglobulin production, (3) increased intracellular degradation, or (4) rapid extracellular degradation of abnormal immunoglobulins. Interestingly, the light chain is of k type in about 75% of patients with nonsecretory myeloma.

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