What are-defining events in multiple myeloma?

Updated: May 11, 2021
  • Author: Dhaval Shah, MD; Chief Editor: Emmanuel C Besa, MD  more...
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Myeloma-defining events include the following [2] :

  • Serum calcium level >0.25 mmol/L (>1 mg/dL) higher than the upper limit of normal or >2.75 mmol/L (>11 mg/dL)
  • Renal insufficiency (creatinine >2 mg/dL [>177 μmol/L] or creatinine clearance < 40 mL/min)
  • Anemia (hemoglobin < 10 g/dL or hemoglobin >2 g/dL below the lower limit of normal)
  • One or more osteolytic bone lesions on skeletal radiography, CT, or PET-CT
  • Clonal bone marrow plasma cells ≥60%
  • Abnormal serum free light chain (FLC) ratio ≥100 (involved kappa) or < 0.01 (involved lambda)
  • One or more focal >5 mm lesions on MRI scans

Active disease may also be indicated by repeated infections, amyloidosis, or hyperviscosity.

Indolent and smoldering multiple myeloma

Indolent MM is a subset of MM with the following features:

  • Bone disease absent (or very limited)
  • Performance status greater than 70%
  • Hemoglobin level greater than 10 g/dL
  • Serum calcium level within the reference range
  • Creatinine level < 2 mg/dL
  • No infections
  • Low M protein levels (ie, < 7 g/dL for IgG, < 5 g/dL for IgA)

Smoldering (asymptomatic) MM is similar to indolent MM. Diagnostic criteria for smoldering MM are as follows [2] :

  • Serum monoclonal protein: IgG or IgA ≥3 g/dL, or
  • Bence-Jones protein ≥500 mg/24 h and/or
  • Clonal bone marrow plasma cells 10%–60% and
  • Absence of myeloma-defining events or amyloidosis

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