Differential Diagnosis
Plasmacytoma / Myeloma Reactive Plasmacytosis
Light chain restriction by flow cytometry, immunohistochemistry or in situ hybridization
No light chain restriction
Plasmacytoma Myeloma
Single osseous or extraosseus lesion
Lytic bony lesions
No increase away from lesion
Usually increased plasma cells on random bone marrow biopsy
No end-organ damage
May have end-organ damage
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
Plasmacytoma / Myeloma Lymphoplasmacytic Lymphoma and Nodal , Extranodal and Splenic Marginal Zone Lymphomas
Plasma cells may be pleomorphic or plasmablastic
Plasma cell component usually not markedly atypical
Uniform plasma cell morphology
Plasma cells mixed with small lymphocytes
IgG or IgA M component most common
IgM or IgG M component most common
CD20 often negative
CD20 80%
Uniformly CD138 positive
Scattered CD138 positive cells
Often CD56+, CD19-, CD45-
CD56-, CD19+, CD45+
Plasmablastic Lymphoma Anaplastic (Plasmablastic) Plasmacytoma /Myeloma
Plasmablastic morphology
Subset plasmablastic
Often HIV+ or otherwise immunosuppressed
Usually not immunosuppressed
Often in oral cavity or mucosal areas of head
Extraosseous sites overlap
~60% EBV+
usually EBV negative
Plasmacytoma and plasmablastic lymphoma have the same immunophenotype, other than EBV and are generally separated based on clinical grounds
