monoclonal gammopathy of undetermined significance

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Monoclonal gammopathy of undetermined significance (MGUS) is the most common plasma cell disorder and refers to the presence of an abnormal monoclonal antibody in the blood but the absence of the overt bone marrow and clinical signs of multiple myeloma.

Epidemiology

MGUS is the most common plasma cell disorder, is present in 3-4% of patients over the age of 50 years . MGUS prevalence increases with advancing age .

Clinical presentation

The condition is asymptomatic.

Diagnostic criteria

The criteria for MGUS diagnosis according to the International Myeloma Working Group include :

  • serum M-protein <3 g/dL
  • clonal plasma cell population present in the bone marrow (<10% cellularity)
  • absence of end-organ damage (e.g. hypercalcemia, renal insufficiency, lytic lesions, anemia)

Pathology

Genetic changes including hyperdiploidy, IgH translocations, and cyclin D gene dysregulation seem to be important in the transition from a normal plasma cell to a pre-malignant plasma cell such as that found in MGUS or smoldering myeloma . Clonal expansion of a single pre-malignant plasma occurs which produces excess paraprotein of one of the immunoglobulin types (e.g. IgG, IgM). However, further changes are needed to transition into a myeloma cell .

Ninety-percent of multiple myeloma patients are seen to have been in an MGUS phase before transitioning into multiple myeloma . Factors that predict an increased risk of multiple myeloma progression from MGUS include non-IgM MGUS and paraprotein levels over 1.5 g/dL .

Radiographic features

Plain radiograph and CT

Osteoporosis and vertebral fractures are more common in MGUS patients than in healthy controls .

MRI

MRI is not indicated in the initial workup of MGUS patients unless there is an increased suspicion of multiple myeloma progression .

MGUS patients usually will have a normal-appearing bone marrow:

  • T1: hyperintense
  • T2: hypointense

However, focal lesions that may represent infiltration by monoclonal plasma cells may be present and these patients have an increased risk of transforming into multiple myeloma .

Treatment and prognosis

MGUS patients are generally under surveillance with regular repeat blood tests and imaging. 20% of MGUS patients will progress to multiple myeloma, amyloidosis, or a lymphoproliferative disorder within 25 years, with up to 1% of patients with MGUS transitioning into multiple myeloma per year .

Complications

History and etymology

The condition now known as MGUS was first described by the Swedish physician Jan Walderström (1906-1996) in 1961 and termed "essential benign hypergammaglobulinemia" . The term MGUS first appeared in 1978 .

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