A bone marrow biopsy from a 65-year-old man with unexplained anemia shows increased plasma cells (>60%) with a monotypic kappa light chain. His serum protein electrophoresis reveals an M-spike in the gamma region. Serum free light chain ratio is markedly abnormal. According to IMWG 2014 criteria, which single finding alone qualifies as a 'myeloma-defining event' without end-organ damage?
- A Serum M-protein ≥3 g/dL
- B Bone marrow plasma cells ≥60% ✓
- C Bence-Jones proteinuria >1 g/24h
- D Serum beta-2 microglobulin elevation
Correct answer: B. Bone marrow plasma cells ≥60%
Explanation
The IMWG 2014 revised criteria added 'SLiM-CRAB' myeloma-defining events to allow treatment before overt end-organ damage. The 'SLiM' biomarkers are: bone marrow plasma cells ≥60% ('S' is for sixty), serum involved/uninvolved free light chain ratio ≥100 ('Li'), and >1 focal lesion on MRI ('M'). Serum M-protein ≥3 g/dL alone indicates smoldering myeloma, not active myeloma.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.