Monoclonal Gammopathy of Undetermined Significance
Supplemental Studies
Immunohistology and Flow Cytometry
- Plasma cell quantitation is best performed by differential count on the bone marrow aspirate or by immunohistochemistry on the bone marrow biopsy.
- Flow cytometry may significantly underestimate plasma cell percentage, but does establish clonality.
Hematolymphoid markers
- CD45 absent or dim in >99%
B cell and plasma cell markers
- CD138 >99%
- CD38 >99%
- CD79a most
- CD20 variable, often absent
- CD19 variable, often absent
- CD56 10-60%, weak (aberrant, but may be seen in reactive conditions)
- Cytoplasmic kappa or lambda light chain by flow cytometry, in situ hybridization, or immunohistochemistry
Cytogenetics
- IgG/IgA MGUS: hyperdiploidy, translocations involving 14q32, deletion 13q
- Not useful prognostically or in differential diagnosis from plasma cell myeloma
- FISH (fluorescence in situ hybridization) much more sensitive than karyotyping
Useful Laboratory Tests
- Serum or urine protein electrophoresis, immunofixation, light chain quantification
- Quantitation and typing of monoclonal immunoglobulin / light chain
- 70% IgG, 15%IgM, 12% IgA
- Serum free light chain analysis may be required to demonstrate clonal light chains
- These studies may be used to
- Establish presence of a monoclonal plasma cell population
- Quantitation helps subtype the plasma cell dyscrasia (i.e. >3g/dL serum monoclonal protein is a major criterion for myeloma)
- Track disease burden over time
