In 1978, the term "monoclonal gammopathy of undetermined significance" (MGUS) was introduced. MGUS is defined as a serum monoclonal (M) protein less than 3.0 g/dL; less than 10% plasma cells in the bone marrow, if done; little or no M protein in the urine; and absence of lytic bone lesions, anemia, hypercalcemia or renal insufficiency. This article discusses the recognition, prevalence, natural history, and progression of MGUS. Management of the disease is discussed along with its association with other disorders. Information on smoldering multiple myeloma is included.
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