Differential Diagnosis
Symptomatic Plasma Cell Myeloma Asymptomatic / Smoldering Myeloma MGUS
Usually but not always >10% clonal plasma cells in bone marrow or plasmacytoma
** ≥10% clonal plasma cells in bone marrow AND/OR
<10% clonal plasma cells in bone marrow
M protein in serum or urine or free light chain in urine
Serum M-protein >3g/dL
Serum M-protein <3g/dL
** Lytic bony lesions or end-organ damage (hypercalcemia/ anemia/ renal insufficiency etc)
No lytic lesions or end-organ damage
No lytic lesions or end-organ damage
** Critical points: bone marrow plasma cells or M-protein above threshholds separates asymptomatic myeloma from MGUS and bone or other end organ damage separates symptomatic from asymptomatic myeloma
MGUS Lymphoplasmacytic Lymphoma , Chronic Lymphocytic Leukemia or Other Low Grade B Cell Lymphoma with M-protein
Uniform plasma cell morphology
Lymphoid component present
CD20 often negative
CD20 usually uniformly positive
Uniformly CD138 positive
Scattered CD138 positive cells in plasmacytoid component
MGUS Reactive Plasmacytosis
Light chain restriction by flow cytometry, immunohistochemistry or in situ hybridization
No light chain restriction
Aberrant immunophenotype (e.g. CD56+, CD19-)
CD19+, CD56-
Myeloma-associated cytogenetic abnormalities by FISH in >50%
Normal cytogenetics by FISH
