Monoclonal gammopathy of undetermined significance

Monoclonal gammopathy of unknown significance (MGUS):

Monoclonal (M) protein in the serum (<3 g/dL) or in urine (<500 mg per 24 hours)
Bone marrow clonal cells <10% (a bone marrow exam is only required if M protein is >1.5 g/dL, or for non-IgG MGUS, or if the free light chain ratio is abnormal)
Absence of signs of end-organ damage that can be attributed to the plasma cell proliferative process (e.g., hypercalcemia, renal insufficiency, anemia, bone lesions, or amyloidosis).

Asymptomatic (smoldering) myeloma:

M protein in the serum (≥3 g/dL) or in urine (≥500 mg per 24 hours), and/or bone marrow clonal cells 10% to 60%
Absence of signs of end-organ damage that can be attributed to the plasma cell proliferative process (e.g., hypercalcemia, renal insufficiency, anemia, bone lesions, or amyloidosis).

Active (symptomatic) myeloma:

Bone marrow clonal cells ≥10%, or biopsy-proven bony or extramedullary plasmacytoma, and 1 or more of the following:
- Evidence of end-organ damage that can be attributed to the plasma cell proliferative process (e.g., hypercalcemia, renal insufficiency, anemia, bone lesions, or amyloidosis)
- Bone marrow clonal cells ≥60%
- Involved:uninvolved serum free light chain ratio ≥100
- >1 focal lesion (5 mm or more in size) on magnetic resonance imaging studies
Presence of M protein in serum or urine in addition to the above criteria indicates secretory myeloma.

Solitary plasmacytoma and systemic immunoglobulin light chain amyloidosis are also defined as distinct entities.

The Mayo Clinic has developed a risk-stratification model for disease progression based on 3 adverse risk factors:

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Criteria