From the Guidelines
Monoclonal Gammopathy of Undetermined Significance (MGUS) is defined by a M-protein less than 30 g/L, bone marrow plasma cell percentage less than 10%, and absence of signs or symptoms related to multiple myeloma or other lymphoproliferative malignancies. This definition is based on the most recent and highest quality study available, which provides a clear and concise criteria for diagnosing MGUS 1. The study, published in Haematologica in 2014, highlights the importance of distinguishing MGUS from other related disorders, such as multiple myeloma and Waldenström’s macroglobulinemia.
Key Characteristics of MGUS
- M-protein level less than 30 g/L
- Bone marrow plasma cell percentage less than 10%
- Absence of signs or symptoms related to multiple myeloma or other lymphoproliferative malignancies
- Average risk of progression to multiple myeloma or other lymphoproliferative disorders of 1% per year
Types of MGUS
- IgG and IgA MGUS: defined by a M-protein less than 30 g/L and bone marrow plasma cell percentage less than 10%
- IgM MGUS: defined by the presence of an IgM M-protein without bone marrow infiltration by lymphoplasmacytic lymphoma
- Light-chain MGUS: defined by an abnormal κ/λ free light-chain ratio and increase in concentration of the involved light-chain The study also notes that understanding MGUS is crucial for early detection of progression to malignancy, allowing for timely intervention and improved outcomes 1. Another study published in Leukemia in 2010 provides additional guidance on the risk factors for progression and guidelines for monitoring and management of MGUS, but the definition and criteria provided in the 2014 study are more recent and of higher quality 1.
From the Research
Definition of MGUS
- Monoclonal gammopathy of undetermined significance (MGUS) is a premalignant plasma cell dyscrasia that consistently precedes multiple myeloma (MM) with a 1% risk of progression per year 2.
- MGUS is defined as a serum M protein level of less than 3 g/dL, less than 10% clonal plasma cells in the bone marrow, and the absence of end-organ damage 3.
- MGUS may progress to multiple myeloma, AL amyloidosis, Waldenström macroglobulinemia, or lymphoma 3.
Characteristics of MGUS
- IgG and IgA MGUS are precursor conditions of multiple myeloma (MM), whereas light-chain MGUS is a precursor condition of light chain MM 4.
- IgM MGUS is a precursor condition of Waldenström macroglobulinemia (MW) or other lymphoproliferative diseases 4.
- The prevalence of MGUS is 3.2% in the white population but is approximately twice that high in the black population 3.
Risk Stratification of MGUS
- Risk factors for progression include the size of the serum M protein, the type of serum M protein, the number of plasma cells in the bone marrow, and the serum free light chain ratio 3.
- Three risk stratification models have been constructed that are useful in daily practice for predicting risk of progression of MGUS into malignant forms of monoclonal gammopathy - MAYO, PETHEMA and CMG model 4.
- The goal of all three models is to identify correctly prognostic markers that can divide patients into low-risk MGUS and high-risk MGUS groups 4.