Hematology and Oncology Book

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Monoclonal Gammopathy of Undetermined Significance

Aka: Monoclonal Gammopathy of Undetermined Significance, MGUS
  1. See Also
    1. Monoclonal Gammopathy (Plasma Cell Disorder)
    2. Multiple Myeloma
    3. Hematologic Cancer
  2. Epidemiology
    1. Ultimately responsible for 20% of Multiple Myeloma cases after progression
    2. Age
      1. Present in 2-3% of patients over age 50 years (increases to 5% in age over 70 years old)
    3. Gender
      1. More common in men
    4. Race and ethnicity
      1. More common in black patients than white patients
  3. Evaluation: Factors suggesting higher risk of Multiple Myeloma progression
    1. Criteria
      1. Elevated M Protein Level 1.5 to 3 g/dl (levels >3 g/dl consistent with Multiple Myeloma)
      2. Non-IgG MGUS
      3. Abnormal free light chain ratio
    2. Distinguishing features from Multiple Myeloma
      1. Bone Marrow plasma cells <10%
      2. Asymptomatic with no end-organ damage (see CRAB Criteria in Monoclonal Gammopathy)
    3. Interpretation
      1. Risk of Multiple Myeloma is 58% in 20 years if all 3 factors present
  4. Associated Conditions: MGUS Progression to other Plasma Cell Disorders
    1. Multiple Myeloma (RR 23.9)
    2. Immunoglobulin light chain Amyloidosis (RR 8.8)
    3. Macroglobulinema (RR 47.6)
    4. Plasmacytoma (RR 12.7)
  5. Monitoring
    1. Low risk of progression (5% risk of progression)
      1. Criteria (No risk factor present)
        1. M-Spike <1.5 g/L
        2. IgG type
        3. Free light chain ratio normal
      2. Evaluation and Management
        1. No additional work-up (including no bone imaging)
        2. Repeat SPEP in 6 months and then every 2-3 years indefinately
    2. Intermediate risk of progression (21-37% risk of progression)
      1. Criteria (1-2 risk factors present)
        1. M-Spike >1.5 g/L OR
        2. Non-IgG type OR
        3. Free light chain ratio abnormal (involved to uninvolved >100)
      2. Evaluation and Management
        1. Hematology referral
        2. Bone Marrow Biopsy
        3. Bone imaging
        4. Repeat SPEP in 6 months and then every year indefinately
    3. High risk of progression (58% risk of progression)
      1. Criteria (all 3 risk factors present)
        1. M-Spike >1.5 g/L AND
        2. Non-IgG type AND
        3. Free light chain ratio abnormal (involved to uninvolved >100)
      2. Evaluation and Management
        1. Hematology referral
        2. Bone Marrow Biopsy
        3. Bone imaging
        4. Repeat SPEP in 6 months and then every year indefinately
  6. Course
    1. Progresses to Multiple Myeloma in 1% of cases per year
  7. References
    1. Thompson (2017) Monoclonal Gammopathy, Mayo Clinical Reviews, Rochester, MN

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