Monoclonal gammopathy of unclear significance (MGUS) is detected at high frequency in a variety of disciplines as an incidental finding. MGUS can be associated with non-malignant diseases, but it also can be a precursor of malignant lymphoproliferative disorders (multiple myeloma, Waldenstroem's disease, other non-Hodgkin's lymphoma, light chain (AL) - amyloidosis). However, many of these patients remain asymptomatic throughout their lives. Screening is performed by serum protein electrophoresis, immunofixation and determination of quantitative immunoglobulins and free light chains in serum. Currently, general population screening is not recommended. There are three subtypes with different rates and types of progression: IgM-MGUS, non-IgM-MGUS, and light-chain MGUS. The scope of further diagnostics and follow-up is based on the clinical findings and risk stratification (monoclonal protein in serum < or ≥ 15 g/l and normal or abnormal free light chain ratio in serum). If paraprotein-associated disease is detected, gammopathy is of clinical significance and should not be referred to as MGUS.
