However, more sensitive methods of detecting urinary and serum light chain myeloma proteins using enzyme-linked immunosorbent assays indicate that >60% of cases initially diagnosed as non-secretory multiple myeloma had abnormal levels of either a clonal κ or λ light chain in their urine or serum and therefore were better diagnosed as having light chain multiple myeloma. Based on the latter definition, non-secretory multiple myeloma represents ~1% of all multiple myeloma cases with formerly diagnosed non-secretory myelomas considered to be cases primarily of light chain multiple myeloma but on occasion "false non-secretors", i.e. cases in which there is evidence of myeloma protein secretion such as renal myeloma protein deposits.A Mayo Clinic study of 124 patients initially diagnosed as having non-secretory multiple myeloma were later found to be composed of 65% free light chain secretors and 35% true non-secretors. As a group, these patients response to therapy, time to disease recurrence, and overall survival were similar to typical myeloma patients. However, in a subset of patients diagnosed after 2001 and therefore treated with more effective therapy that included autologous stem-cell transplantation, prognosis was significantly better in non-secretory multiple myeloma patients (median survival 8.3 years) compared to typical myeloma patients (median survival 5.4 years). In addition, non-secretory patients exhibited a better prognosis than light chain-secretory patients.
While its presentations and findings are similar to solitary plasmacytoma, solitary plasmacytoma with minimal bone marrow involvement is more likely to progress, i.e. it recurs or becomes overt multiple myeloma in 20% to 60% of cases within 3 years. Solitary plasmacytomas associated with 10% or more plasma cells are diagnosed as overt multiple myeloma. Non-secretory multiple myeloma
Non-secretory multiple myeloma represents a class of plasma cell dyscrasias where no myeloma protein is detected in serum or urine of patients with evidence of increased clonal bone marrow plasma cells and/or multiple plasmacytomas, particularly of the bone but also of soft tissues. While a pre-malignant phase is likely, most new cases of non-secretory multiple myeloma are brought to attention not because of incidental M protein detection which by definition is absent but because of patient symptoms indicative of malignancy possibly of plasma cell origin. The condition has been diagnosed based on biopsy-proved clonal plasma cell tumors and/or the presence in bone marrow of plasma cells at ≥10% of nucleated cells in individuals who have evidence of end organ damage attributable to an underlying plasma cell disorder. These patients typically also show one or more CRAB signs and lack evidence of a myeloma protein as measured by protein electrophoresis and immunofixation.