The Fellow on Call: The Heme/Onc Podcast Episode 141: Myeloma Series, Pt.2 - Intro to MGUS and Smoldering Myeloma (2025)
Dec 10, 2025
Dive into the intriguing world of plasma cell dyscrasias! This discussion unpacks the nuances between MGUS and smoldering myeloma, from risk assessment to monitoring strategies. Learn how free light chains play a role in interpreting results and why a 24-hour urine protein test is crucial. Get insights on the criteria for diagnosing smoldering myeloma, including the SLIM-CRAB metrics. Plus, discover the significant 20-year progression risks of these conditions and the importance of cytogenetic testing in predicting outcomes.
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Always Add Free Light Chains
- Always order serum free light chains with an SPEP to help risk-stratify monoclonal proteins.
- Use the light chain ratio to decide if further workup like bone marrow biopsy or imaging is needed.
Use 24‑Hour Urine, Not Spot Checks
- Obtain a 24-hour UPEP, not a spot urine, to quantify urine monoclonal protein for risk stratification.
- Use the 24-hour value both for diagnosis (e.g., smoldering myeloma) and for future response monitoring.
MGUS Versus Higher Risk Clones
- MGUS is likely when the M-spike is under 3 g/dL and bone marrow plasma cells are under 10%.
- High-risk features are non-IgG type, M-spike >1.5 g/dL, or abnormal FLC ratio outside 0.26–1.65.