From the Guidelines
Diagnosis of Multiple Myeloma
Multiple myeloma cannot be diagnosed with fewer than 10% plasma cells in the bone marrow, according to the International Myeloma Working Group (IMWG) diagnostic criteria, which require 10% or more clonal plasma cells in the bone marrow (and/or a biopsy-proven plasmacytoma) plus any one or more myeloma-defining events (MDE) 1.
Key Diagnostic Criteria
The IMWG diagnostic criteria for multiple myeloma include:
- 10% or more clonal plasma cells in the bone marrow
- Presence of serum and/or urinary monoclonal protein (except in patients with non-secretory multiple myeloma)
- Evidence of end-organ damage, such as hypercalcemia, renal insufficiency, anemia, or bone lesions, which can be attributed to the underlying plasma cell proliferative disorder 1.
- Myeloma-defining events (MDE) include:
- Bone marrow clonal plasma cells ≥60%
- Serum involved to uninvolved free light chain (FLC) ratio ≥100 (provided involved FLC level is ≥100 mg/L)
- More than one focal lesion (5 mm or more in size) on magnetic resonance imaging (MRI) 1.
Importance of Plasma Cell Percentage
While the presence of fewer than 10% plasma cells in the bone marrow does not meet the diagnostic criteria for multiple myeloma, it may be indicative of other plasma cell disorders, such as monoclonal gammopathy of undetermined significance (MGUS) or smoldering multiple myeloma (SMM) 1.
Clinical Implications
In clinical practice, a thorough evaluation, including bone marrow examination, serum and urine protein electrophoresis, and imaging studies, is necessary to diagnose multiple myeloma and distinguish it from other plasma cell disorders 1. The IMWG diagnostic criteria provide a framework for diagnosing multiple myeloma and guiding treatment decisions.
From the Research
Diagnosis of Multiple Myeloma
- The diagnosis of multiple myeloma typically requires the presence of ≥10% clonal bone marrow plasma cells or a biopsy-proven plasmacytoma plus evidence of one or more multiple myeloma defining events (MDE) 2, 3.
- However, a study published in 1993 found that in some cases, multiple myeloma can be diagnosed with fewer than 10% plasma cells in the bone marrow, particularly when immunohistological staining for immunoglobulin light chains is used to assess plasma cell clonality 4.
- Another study published in 1999 noted that patients with less than 10% plasma cells in bone marrow may have monoclonal gammopathy of undetermined significance (MGUS) rather than multiple myeloma, and that these patients should be followed up regularly to monitor for the development of a malignant process 5.
Criteria for Diagnosis
- The presence of fewer than 10% plasma cells in bone marrow is often considered a criterion for MGUS rather than multiple myeloma 5, 6.
- However, the diagnosis of multiple myeloma can be made in patients with fewer than 10% plasma cells in bone marrow if other criteria are met, such as the presence of a biopsy-proven plasmacytoma or one or more MDE 2, 3.
- The use of immunohistological staining for immunoglobulin light chains can help to assess plasma cell clonality and diagnose multiple myeloma in patients with fewer than 10% plasma cells in bone marrow 4.