A 60-year-old man with back pain has lytic lesions on skeletal survey. Urine protein electrophoresis shows a single band that precipitates on heating to 50 degrees Celsius and redissolves on boiling. This finding represents excretion of:
- A Alpha-fetoprotein secreted by coexisting hepatocellular carcinoma
- B Polyclonal intact IgG molecules filtered through damaged glomeruli
- C Monoclonal free immunoglobulin light chains (kappa or lambda) by neoplastic plasma cells ✓
- D Beta-2 microglobulin shed from all nucleated cells in renal failure
Correct answer: C. Monoclonal free immunoglobulin light chains (kappa or lambda) by neoplastic plasma cells
Explanation
The heat precipitation at 40 to 60 degrees Celsius with redissolution at boiling is the classical property of Bence Jones proteins, which are monoclonal free kappa or lambda light chains produced by the malignant plasma cell clone in multiple myeloma. They are detected as an M band on urine electrophoresis. Beta-2 microglobulin is elevated in myeloma but is not heat-precipitable, killing option D.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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