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urine protein electrophoresis immunofixation IgM kappa multiple myeloma Waldenstrom
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multiple myeloma immunofixation electrophoresis IgM band kappa lambda light chain
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GradeResponse
Answer: Multiple Myeloma — IgM (Option 1) ✓
Reading the Electrophoresis Gel
The image shows urine immunofixation electrophoresis (IFE) with 6 lanes:
| Lane | Result |
|---|---|
| SEP (Serum/urine Electrophoresis) | Dense band present — confirms a monoclonal protein |
| IgG | Faint/absent band |
| IgA | Absent band |
| IgM | Moderate band present ✓ |
| K (Kappa) | Strong, dense band ✓ |
| L (Lambda) | Absent band |
Interpretation: There is a monoclonal IgM protein with Kappa light chain restriction in the urine. This pattern = IgM-Kappa M protein.
Why Option 1 (Multiple Myeloma — IgM) is Correct
Key clues in the vignette:
- 72-year-old man
- Generalized anasarca (massive edema) + icterus (jaundice)
- Hepatosplenomegaly
- Deranged kidney function tests (renal involvement)
- Urine gamma-globulins >3 g/dL — massive proteinuria from monoclonal light chains (Bence Jones protein)
- IFE shows IgM + Kappa monoclonal band
The elevated urine gamma-globulins >3 g/dL represent Bence Jones proteinuria — free monoclonal kappa light chains being excreted in urine due to their small size passing through the glomerulus. This, combined with the IgM-Kappa IFE pattern, hepatosplenomegaly, and end-organ damage, points to a plasma cell/lymphoplasmacytic malignancy.
Why Not the Other Options?
| Option | Why Wrong |
|---|---|
| IgA MM | IgA lane on gel shows NO band |
| IgG MM | IgG lane shows no significant band |
| Monoclonal Gammopathy of Undifferentiated Proteins | This term doesn't exist as a standard diagnosis. MGUS (Monoclonal Gammopathy of Undetermined Significance) is a benign, asymptomatic condition — this patient has massive end-organ damage (kidneys, liver), ruling out MGUS |
Important Nuance: IgM Myeloma vs. Waldenström Macroglobulinemia
IgM paraprotein causing organomegaly most commonly suggests Waldenström Macroglobulinemia (WM), which is a lymphoplasmacytic lymphoma. However, the question specifically frames it as "Multiple Myeloma — IgM," which is a rare but recognized entity (~0.5% of myelomas).
The distinguishing feature here is the urine Bence Jones proteinuria >3 g/dL with kappa restriction, which is characteristic of a plasma cell dyscrasia. The gel confirms the IgM-K paraprotein, making Option 1 the best answer among the choices given.
(Harrison's Principles of Internal Medicine, 21st Ed., p. 3335 — workup of clonal paraprotein includes 24-h urine electrophoresis and immunofixation, quantitative Ig levels IgG/IgA/IgM, and serum free light chain ratio)
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