A 58-year-old man is evaluated for back pain. Bone marrow shows 25% clonal plasma cells, serum M-protein is 35 g/L, and the involved to uninvolved free light chain ratio is 40. Hemoglobin is 12.5 g/dL, calcium is 9.2 mg/dL, creatinine is 1.0 mg/dL, skeletal survey shows osteopenia without discrete lytic lesions, and whole body MRI shows no focal lesions. What is the correct diagnosis?
- A Monoclonal gammopathy of undetermined significance
- B Active multiple myeloma requiring immediate therapy
- C Smoldering multiple myeloma ✓
- D Solitary plasmacytoma of bone
Correct answer: C. Smoldering multiple myeloma
Explanation
Smoldering myeloma requires clonal bone marrow plasma cells of 10 to 60 percent plus a serum M-protein of at least 30 g/L or an involved/uninvolved free light chain ratio of at least 100, with no myeloma defining events. This patient meets the M-protein threshold but has no CRAB features, no FLC ratio above 100, fewer than 60 percent plasma cells, and no focal MRI lesion, so he remains smoldering. MGUS requires less than 10 percent plasma cells and M-protein below 30 g/L.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.