What are the diagnostic criteria for monoclonal gammopathy of undetermined significance (MGUS)?

Updated: Dec 29, 2019
  • Author: Suzanne R Fanning, DO; Chief Editor: Emmanuel C Besa, MD  more...
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Monoclonal gammopathy of undetermined significance (MGUS) must be differentiated from myoclonal gammopathy of renal significance (MGRS), multiple myeloma (MM), and smoldering MM (SMM). Criteria for MGUS established by the International Myeloma Working Group [32] and the World Health Organization [33] are as follows:

  • Serum M-protein level < 3 g/dL
  • Bone marrow plasma cells < 10% and low level of plasma cell infiltration in a trephine biopsy specimen
  • No evidence of B-cell proliferative disorder (ie, MM, Waldenström macroglobulinemia, amyloid light-chain amyloidosis)
  • No M-protein or only small amounts of monoclonal light chain in urine
  • No osteolytic lesions, anemia, hypercalcemia, or M-protein–related renal function impairment

In addition to the hematologic abnormalities, MGRS is associated with a wide spectrum of renal diseases, including AL amyloidosis, proliferative glomerulonephritis with monoclonal immunoglobulin deposits, and C3 glomerulopathy with monoclonal gammopathy. Kidney biopsy is indicated in most cases of MGRS, to identify the exact lesion and determine its severity. [5] Treatment to eradicate the underlying clone is indicated; the proteasome inhibitor bortezomib is the preferred therapy in MGRS but a number of other agents have been used in some settings, including rituximab, cytotoxic chemotherapy, and immunomodulatory agents. [34]

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