A 65-year-old man with newly diagnosed multiple myeloma undergoes serum protein electrophoresis. Which is the most common type of monoclonal immunoglobulin produced in multiple myeloma?

Explanation

## Monoclonal Immunoglobulin Types in Multiple Myeloma **Key Point:** **IgG myeloma** is the most common type of monoclonal immunoglobulin in multiple myeloma, accounting for approximately 50–60% of all cases. ### Frequency Distribution of Myeloma Types | Immunoglobulin Type | Frequency | Clinical Features | |---------------------|-----------|------------------| | **IgG** | 50–60% | Most common; can cause hyperviscosity | | **IgA** | 20–25% | Second most common; higher incidence of renal disease | | **IgD** | 2–3% | Rare; often presents with advanced disease | | **IgE** | <1% | Extremely rare; very few cases reported | | **IgM** | <1% | Extremely rare; often classified as Waldenström macroglobulinemia | | **Light chain only** | 10–15% | Bence Jones proteinuria; high renal toxicity | ### Diagnostic Significance ```mermaid flowchart TD A[Suspected Multiple Myeloma]:::outcome --> B[Serum Protein Electrophoresis<br/>Immunofixation]:::action B --> C{Monoclonal spike<br/>identified?}:::decision C -->|IgG 50-60%| D[IgG Myeloma]:::outcome C -->|IgA 20-25%| E[IgA Myeloma]:::outcome C -->|IgD 2-3%| F[IgD Myeloma]:::outcome C -->|Light chain only| G[Light Chain Myeloma]:::outcome D --> H[Assess for complications]:::action E --> H F --> H G --> H ``` **High-Yield:** IgG myeloma is the most common type, followed by IgA. IgD and IgE are rare and often associated with more aggressive disease. IgM is extremely rare in myeloma and should raise suspicion for Waldenström macroglobulinemia instead. **Clinical Pearl:** IgA myeloma has a higher propensity for renal involvement and amyloidosis compared to IgG myeloma. IgD myeloma, though rare, often presents with advanced disease and worse prognosis. Light chain myeloma (Bence Jones proteinuria) carries significant risk of cast nephropathy ("myeloma kidney"). ### Pathophysiological Basis The predominance of IgG reflects the distribution of plasma cells in normal bone marrow, where IgG-producing cells are most abundant. IgA-producing cells are the second most common, explaining the 20–25% frequency of IgA myeloma.