IgG is the Immunoglobulin Most Frequently Increased in Multiple Myeloma
The correct answer is D. IgG is the most frequently increased immunoglobulin in multiple myeloma, accounting for approximately 50-60% of all cases. 1
Distribution of Immunoglobulin Types in Multiple Myeloma
Multiple myeloma is characterized by the proliferation of malignant plasma cells that typically produce a monoclonal immunoglobulin (M-protein). The distribution of immunoglobulin types in multiple myeloma follows a consistent pattern:
- IgG: 50-60% of cases - Most common immunoglobulin type 1, 2
- IgA: 20-25% of cases - Second most common 2
- Light chain only (Bence-Jones): 15-20% of cases - Produces only light chains without heavy chains
- IgD: 2% of cases - Rare
- IgM: 0.5% of cases - Very rare in multiple myeloma (more commonly associated with Waldenström's macroglobulinemia)
- Biclonal gammopathy: 5% of cases - Two different M-proteins present simultaneously 2
- Non-secretory: 3% of cases - No detectable M-protein in serum or urine 1
Diagnostic Significance
The identification of the specific immunoglobulin type is crucial for:
Diagnosis confirmation: The NCCN guidelines specify that detection and characterization of the M-protein by immunofixation is essential for diagnosing multiple myeloma 1
Disease monitoring: The same test must be used for serial studies to ensure accurate relative quantification of the M-protein 1
Risk stratification: Non-IgG myeloma is considered a risk factor for progression in monoclonal gammopathy of undetermined significance (MGUS) 3
Clinical Implications of Immunoglobulin Type
Different immunoglobulin types may be associated with specific clinical features:
- IgG myeloma: Generally has a more indolent course compared to other types
- IgA myeloma: More frequently associated with extramedullary disease
- Light chain myeloma: Higher risk of renal complications and amyloidosis
- IgD myeloma: Often presents with more aggressive disease and poorer prognosis
- IgM myeloma: Extremely rare; must be distinguished from Waldenström's macroglobulinemia
Diagnostic Workup
When evaluating for multiple myeloma, the following tests should be performed to identify and characterize the M-protein:
- Serum protein electrophoresis (SPEP)
- Serum immunofixation electrophoresis (SIFE)
- Quantitative immunoglobulin levels (IgG, IgA, IgM)
- Serum free light chain assay
- 24-hour urine protein electrophoresis (UPEP)
- Urine immunofixation electrophoresis (UIFE)
Conclusion
While multiple myeloma can be associated with various immunoglobulin types, IgG is by far the most common, representing more than half of all cases. This is followed by IgA, while IgM and IgD are rare in multiple myeloma.