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Monoclonal Gammopathy of Undetermined Significance (MGUS)


James R. Berenson

, MD, Institute for Myeloma and Bone Cancer Research

Reviewed/Revised Jun 2023

Monoclonal gammopathy of undetermined significance (MGUS) is the production of M-protein by noncancerous plasma cells in the absence of other manifestations typical of multiple myeloma.

The incidence of monoclonal gammopathy of undetermined significance (MGUS) increases with age, from 1% of people aged 25 years to > 5% of people > 70 years. MGUS may occur in association with other disorders (see table ), in which case M-proteins (monoclonal immunoglobulin proteins, which may consist of both heavy and light chains or of only a light chain) may be antibodies produced in large amounts in response to protracted antigenic stimuli.

Diagnosis of MGUS is usually suspected when the M-protein is incidentally detected in blood or urine during a routine examination. On laboratory evaluation, M-protein is present in lower levels in serum (< 3 g/dL [< 30 g/L]) or urine (< 200 mg/24 hours) than among patients with multiple myeloma. MGUS is differentiated from malignant plasma cell disorders because M-protein levels are lower and lytic bone lesions, anemia, and renal dysfunction are absent. Because of fracture risk, baseline evaluation with a skeletal survey (ie, plain x-rays of skull, long bones, spine, pelvis, and ribs) and bone densitometry should be done. Bone marrow shows only mild plasmacytosis (< 10% of nucleated cells).

Every 6 to 12 months, patients should undergo clinical examination and serum and urine protein electrophoresis to evaluate for disease progression.

NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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