Quantitation of the monoclonal plasma cell component in bone marrow from patients with serum paraproteinemia and nondiagnostic marrow morphology

Diagnostic criteria and histologic grading in multiple myeloma: histologic and immunohistologic analysis of 176 cases with clinical correlation

Diagnostic criteria in myeloma have not been completely standardized or tested for accuracy; furthermore, marrow findings of prognostic value have not been clearly identified. We studied 176 patients with myeloma to determine the relative value of marrow differential, tissue sections, and immunohistology singly or in concert in the diagnosis of myeloma and to correlate morphologic features with prognosis. Controls were patients with benign marrow plasmacytosis. Homogeneous nodules of plasma cells at least 1/2 high-power field and/or monotypic aggregates of plasma cells filling at least one interfatty marrow space correctly identified myeloma in 83.5% of cases, with no false positives. The current numerical criteria of marrow plasmacytosis > or = 10% occurred in 17.1% of the controls, and 39.7% of patients with myeloma had less than 10% marrow plasmacytosis at presentation. Myeloma was graded histologically into categories of none/minimal, moderate, and marked dysplasia on the basis of dysplastic features and mitoses; these categories correlated well with clinical outcome, with median length of survival of 32.9, 25.2, and 12.9 months, respectively (overall median length of survival of 123 patients with myeloma, 29.2 months). Packing of marrow by tumor and mitoses measuring at least 5/high-power field regardless of grade also was associated with a poor prognosis (median lengths of survival, 15.2 and 11 months, respectively). Myeloma may be diagnosed in the great majority of cases by demonstrating homogeneous nodules and/or monotypic aggregates of plasma cells in the marrow. Prognostic features were shown to include marked dysplasia, mitoses, packing of marrow by tumor, and clinical stage.

The value of the bone marrow plasma cell cytoplasmic light chain ratio in differentiating between multiple myeloma and monoclonal gammopathy of undetermined significance

We compared the plasma cell light chain ratios in the bone marrows of 13 patients with multiple myeloma (MM), with those of 13 patients with monoclonal gammopathy of undetermined significance (MGUS). The mean light chain ratio in favour of the paraprotein isotype in the myeloma group was 51.83 (95% confidence limits (CL) 29.52-74.14), while in the MGUS group it was 5.30 (CL 2.07-8.52). The difference between the MGUS and MM groups was significant (p = 0.0005). Neither the bone marrow plasma cell count nor the paraprotein level were significantly correlated with the light chain ratio in either of these two groups. We found a cut-off ratio of 8 to be the most useful in differentiating between myeloma and MGUS. Only one patient with myeloma had a ratio below 8, and one MGUS patient had a ratio above this cut-off point. We conclude that determination of the bone marrow plasma cell light chain ratio is a simple and useful test in differentiating between myeloma and MGUS in difficult cases.

Light chain restriction analysis of bone marrow plasma cells in patients with MGUS or 'solitary' plasmacytoma: diagnostic value and correlation with clinical course

Twenty-eight patients with a diagnosis of 'solitary' plasmacytoma or with gammopathy but with nondiagnostic morphologic examination of the bone marrow were investigated using a short-term bone marrow culture technique which enriched for the plasma cell fraction. The percentage of monotypic plasma cells in these plasma cell enriched cultures was correlated with the subsequent clinical course. The majority of patients with plasmacytoma and a significant number of those with gammopathy but with otherwise non-diagnostic investigations were found to have a monoclonal plasma cell component of greater than 20%. There was a significant correlation between the percentage of monoclonal plasma cells as detected by bone marrow culture and subsequent progression to disseminated myeloma. These results indicate that early bone marrow involvement can be detected by means of plasma cell culture prior to morphologic identification of marrow plasmacytosis and that short-term plasma cell culture distinguishes patients with early, low bulk myeloma from those with monoclonal gammopathy of uncertain significance (MGUS).

Circulating monotypic B-cells in multiple myeloma: association with lambda paraproteins

The peripheral blood and bone marrow mononuclear cell immunophenotype was investigated in series of 41 patients with plasma cell dyscrasias (29 with multiple myeloma and 12 with monoclonal gammopathy of undetermined significance (MGUS) or solitary plasmacytoma). A statistically significant relationship between the presence of monotypic B-cells (MBC) in the peripheral blood and the paraprotein light chain isotype was found in the myeloma patients (P = 0.0025). MBCs were documented in 71% of patients with lambda paraproteins, compared with only 13% of patients with kappa paraproteins. The difference in MBC was independent of disease stage as well as of individual prognosticators such as haemoglobin, renal function, paraprotein size and beta-2-microglobulin, although lambda producers had significantly higher calcium levels than patients with kappa paraproteins (P = 0.03). A similar trend was also noted for MBC to be found more commonly in patients with lambda producing MGUS and solitary plasmacytoma. This phenomenon may account for the worse prognosis in patients with lambda paraproteins. In our hands, immunophenotypic detection of peripheral blood involvement in plasma cell dyscrasias is more sensitive than investigation of karyotype or immunoglobulin gene rearrangements.