2020 Dec 14. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan–.
Monoclonal gammopathy of undetermined significance (MGUS) is an asymptomatic premalignant plasma cell disorder that is characterized by the presence of serum M-protein less than 30 g/L or 3g/dL, bone marrow (BM) clonal plasma cells less than 10%, absence of plasma cell myeloma (PCM) related end-organ damage (CRAB symptoms: hypercalcemia, renal insufficiency, anemia and, bone lesions) and absence of B-cell lymphoma or other disease known to produce an M-protein. MGUS is generally considered a preneoplastic disorder that does not always progress to overt malignancy. There are three distinct types of MGUS
IgM MGUS: Non-IgM MGUS (IgG, IgA, IgD) accounts for the majority of MGUS cases and is characterized by a monoclonal plasma cell.
Non-IgM MGUS may progress to a malignant plasma cell neoplasm. IgM MGUS may develop into Waldenstrom macroglobulinemia, immunoglobulin light chain (AL) amyloidosis, or lymphoma. Light chain MGUS (LC-MGUS) is characterized by a monoclonal protein that lacks the immunoglobulin heavy chain component. LC-MGUS may show progression to idiopathic Bence Jones proteinuria, light chain PCM, AL amyloidosis, or light chain deposition disease. According to a population-based cohort study, the risk of progression to multiple myeloma in patients with light-chain MGUS is 0.3%