IgM Monoclonal Gammopathy of Undetermined Significance

IgM MGUS is considered as a precursor to lymphplasmacytic lymphoma (LPL) and/or Waldenstrom and is separate from Non-IgM MGUS (IgG, IgA), which is a precursor to plasma cell myeloma.  

2016 WHO Diagnostic Criteria

• Serum IgM monoclonal protein <3 g/dL
• <10% bone marrow lymphoplasmacytic infiltrate
• No evidence of the following due to an underlying lymphoproliferative disorder
  • Anemia
  • Hyperviscosity
  • Lymphadenopathy or splenomegaly
  • End-organ damage

Cases fall short of the diagnosis of lymphoplasmacytic lymphoma (LPL), plasma cell myeloma (very rare cases are IgM), or lymphoproliferative disorder with plasmacytic differentiation.

• Clonal B-cells are identified in up to 75% of the cases.
• 50% have a MYD88 L265P mutation.
• 20% have a CXCR4 S338X mutation.
• Patients progress to amyloidosis or LPL/B-cell lymphoproliferative disorder at a rate of 1.5 per year.

References