Diagnosis of Multiple Myeloma: Required Criteria
The correct answer is F: One of the above. For the diagnosis of multiple myeloma, you need ≥10% clonal plasma cells in the bone marrow PLUS evidence of at least ONE (not all) of the CRAB criteria—hypercalcemia, renal insufficiency, anemia, or bone lesions—that is attributable to the underlying plasma cell disorder 1, 2.
Understanding the Diagnostic Framework
The diagnosis of symptomatic multiple myeloma requires two components:
Component 1: Clonal Plasma Cell Evidence
- ≥10% clonal plasma cells on bone marrow examination, OR
- Biopsy-proven plasmacytoma (bony or extramedullary)
Component 2: Myeloma-Defining Event (At Least ONE Required)
CRAB Criteria (any single one suffices):
- C (Hypercalcemia): Serum calcium >11.5 mg/dL (or >11.0 mg/dL per some sources) 1
- R (Renal insufficiency): Serum creatinine >2 mg/dL OR creatinine clearance <40 mL/min 1, 2
- A (Anemia): Hemoglobin value ≥2 g/dL below the lower limit of normal OR hemoglobin <10 g/dL (normochromic, normocytic) 1
- B (Bone lesions): Lytic lesions, severe osteopenia, or pathologic fractures 1
OR any of these biomarkers of malignancy:
- ≥60% clonal bone marrow plasma cells
- Involved/uninvolved serum free light chain ratio >100
1 focal lesion on MRI (each ≥5 mm) 2
Critical Distinction: Why Not "All of the Above"
This is the key clinical pitfall: Multiple myeloma does NOT require all four CRAB features to be present simultaneously. A patient with only anemia and ≥10% plasma cells has multiple myeloma. A patient with only bone lesions and ≥10% plasma cells has multiple myeloma. The presence of ANY SINGLE myeloma-defining event is sufficient 1, 2.
Differential Diagnosis Context
This distinction separates multiple myeloma from its precursor conditions:
- MGUS: <10% plasma cells AND no CRAB features
- Smoldering Multiple Myeloma: ≥10% plasma cells (or M-protein ≥3 g/dL) BUT no CRAB features or biomarkers of malignancy 1, 2
- Multiple Myeloma: ≥10% plasma cells AND at least ONE CRAB feature (or biomarker of malignancy) 1, 2
The updated 2014 IMWG criteria 2, 3 expanded the definition to include specific biomarkers because patients with these features have near-inevitable progression to end-organ damage, making early diagnosis and treatment beneficial for morbidity and mortality outcomes.
In clinical practice: Once you document ≥10% clonal plasma cells, systematically evaluate for each CRAB criterion. Finding even one positive criterion establishes the diagnosis and triggers the need for treatment, as symptomatic myeloma requires immediate therapy to prevent further organ damage and improve quality of life 1.