Monoclonal gammopathy of undetermined significance

INTRODUCTION

Monoclonal gammopathy of undetermined significance (MGUS) is an asymptomatic genetically malignant but clinically premalignant clonal plasma cell proliferative disorder. It occurs in over 3 percent of the general population over the age of 50. It is typically detected as an incidental finding when patients undergo a protein electrophoresis as part of a work up for a wide variety of clinical symptoms and disorders (eg, peripheral neuropathy, vasculitis, hemolytic anemia, skin rashes, hypercalcemia, elevated sedimentation rate).

Monoclonal gammopathy of undetermined significance (MGUS) will be discussed here [1-3]. Testing for the recognition of serum or urinary monoclonal proteins and a discussion of the clinical features, laboratory manifestations, and diagnosis of multiple myeloma are presented separately. (See "Recognition of monoclonal proteins" and "Clinical features, laboratory manifestations, and diagnosis of multiple myeloma".)

DEFINITION AND INITIAL CONCERNS

Diagnostic criteria — Monoclonal gammopathy of undetermined significance (MGUS) is diagnosed by meeting the following three criteria [4,5]:

• The presence of a serum monoclonal protein (M-protein, whether IgA, IgG, or IgM), at a concentration <3 g/dL. The M-protein is detected with serum protein electrophoresis followed by immunofixation for the identification of the M-protein type (figure 1 and figure 2) [6]. It must be distinguished from a polyclonal gammopathy (figure 3). (See "Recognition of monoclonal proteins".)

• Fewer than 10 percent clonal plasma cells in the bone marrow
• The absence of lytic bone lesions, anemia, hypercalcemia, and renal insufficiency related to the plasma cell proliferative process