Smouldering Myeloma
Smouldering myeloma differs from MGUS and myeloma based on specific criteria as shown in Table 4. Smouldering myeloma patients do not require immediate treatment but do require regular follow-up. Around half of people diagnosed with smouldering myeloma will progress to active myeloma or AL amyloidosis within the first five years after their diagnosis.
Table 4: Diagnostic criteria for MGUS, smouldering myeloma and myeloma
| MGUS | Smouldering myeloma | Myeloma |
|---|---|---|
| Serum M protein < 30g/L or elevated serum free light chains (SFLC) | Serum M protein > 30g/L and/or urine M protein > 500mg/24 hours | No criteria* |
| Clonal bone marrow plasma cells < 10% | Clonal bone marrow plasma cells between 10 – 60% | Clonal bone marrow plasma cells > 10% |
| No myeloma defining events or amyloidosis | No myeloma defining events or amyloidosis | One or more myeloma defining events |
*No criteria for serum/urinary M protein or SFLC levels to account for non-secretory myeloma
Guidance now states that patients with newly diagnosed smouldering myeloma should be risk assessed at diagnosis using either the Mayo 20-2-20 or IMWG 20-2-20 model, which both aim to identify those at greatest risk of progression at 2 years. This can help guide management e.g. how often imaging should be carried out and an awareness of infection risk, and in the case of high-risk patients, a consideration for entry into clinical trials. Both center around the following factors with the IMWG model also taking into account chromosomal abnormalities:
- Serum M-protein >2g/dL
- Bone barrow plasma cell (BMPC) infiltration >20% and/or
- Ratio of involved vs uninvolved sFLC >20
A key point for routine practice is the recommendation that the terms smouldering myeloma and myeloma are used, as defined in the table above, rather than the previous terms asymptomatic and symptomatic. This is because the terms asymptomatic and symptomatic myeloma can be misleading because not all patients with a myeloma defining event will present with clinical signs or symptoms.