Differentiation of monoclonal gammopathy of undetermined significance and multiple myeloma using flow cytometric characteristics of plasma cells

Background and Objectives. The differential diagnosis between multiple myel oma (MM) and monoclonal gammopathy of undetermined significance (MGUS) may be uncertain in some cases; this problem is reflected by discrepancies betw een different classification systems with an accordance in only 2/3 of case s. We studied whether-flow cytometric characteristics of plasma cells (PC) can be used for the differentiation between MGUS and MM. Design and Methods , Patients were divided into 3 groups: Group A included 13 myeloma patients with a plasma cell infiltration of the bone marrow of 10-30%, serum M-prot ein less than or equal to 3.5 g/dL (IgG) or less than or equal to 2 g/dL(Ig A) and without bone lesions in conventional radiography. Group B consisted of 53 patients who fulfilled the Durie and Salmon diagnostic criteria inclu ding at least one major criterion, and group C was formed of individuals wi th MGUS (n=17). The ratio of immunophenotypically normal (.e. CD19(+)/CD56( -)) to all bone marrow plasma cells (BMPC), the number of peripheral blood PC (PBPC), the percentage of BMPC in S-phase and the DNA content of BMPC we re analyzed. Results. All individuals with MGUS and no patient with MM in g roup A or group B had a ratio of phenotypically normal to all BMPC greater than or equal to 20%. The median of monoclonal PBPC was 0/muL (range 0-2/mu L) in MGUS, 1/muL (range 0-30/muL) in MM group A and 2.4/muL (range 0-211/m uL) in MM group B. The median percentage of BMPC in S-phase was 1.6% in bot h MGUS and group A and 3% in group B. Aneuploidy was found in 12%, 11% and 41% in MGUS, group A and group 13, respectively. Interpretation and Conclus ions, The ratio of immunophenotypically normal to all BMPC was the only flo w cytometric parameter for the differentiation of MGUS and MM group A (p <0 .0005). The other parameters were significantly different between MGUS and MM group 13, but not group A. (C) 2001, Ferrata Storti Foundation.