According to the International Myeloma Foundation, the definition of MM is ≥ 10% clonal bone marrow plasma cells or a biopsy-proven plasmacytoma plus the presence of one or more calcium elevation, renal insufficiency, anemia, and bone abnormalities (CRAB) features and myeloma-defining events (MDEs).
This is a revision from the previous criteria for the diagnosis of MM that required the CRAB criteria for the presence of end-organ damage. CRAB includes increased calcium levels, renal dysfunction, anemia, and destructive bone lesions. MDE incorporates three specific biomarkers: bone marrow clonal plasmacytosis ≥ 60%, serum involved/uninvolved free light chain (FLC) ratio ≥ 100 (provided involved FLC is ≥ 100 mg/L), or more than one focal lesion on MRI (of at least 5 mm).
Smoldering multiple myeloma can have a bone marrow percentage from 10% to 60%. A bone marrow percentage of < 10% is considered monoclonal gammopathy of undetermined significance (MGUS), and > 60% is considered active myeloma.
Figure 1. Multiple myeloma, bone marrow radiograph, frontal view, right side of thorax. Multiple myeloma is a neoplastic disease involving proliferation of malignant plasma cells in the bone marrow and characterized by widespread osteolytic lesions.
Learn more about the management of MM.
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Cite this: Joshua Richter, Emmanuel C. Besa. Fast Five Quiz: Multiple Myeloma Management - Medscape - May 16, 2023.
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