Monoclonal gammopathy of undetermined significance (MGUS): where is the hidden danger? Definition and work-up

Monoclonal gammopathy of undetermined significance (MGUS) is a premalignant hematological condition arising from B‑cells, characterized by the presence of monoclonal immunoglobulin production, also known as paraprotein. It is found in up to 3% of individuals over the age of 50 years. The overall progression rate is low at around 1% per year, with most patients progressing to multiple myeloma (MM). Other diseases that may arise from MGUS include non-Hodgkin lymphomas, Waldenstrom macroglobulinemia, amyloid light-chain (AL) amyloidosis, POEMS (polyneuropathy, organomegaly, endocrinopathy, M‑protein, skin changes), cryoglobulinemia, monoclonal gammopathy of renal significance (MGRS), and additional paraprotein-driven diseases. Every case of monoclonal gammopathy warrants careful investigation to rule out the presence of a malignant form. In recent years, paraprotein-associated conditions such as MGRS have been increasingly recognized. Accurate diagnosis and work-up of these cases require a multidisciplinary approach, and it is paramount to accurately distinguish them from true MGUS in order to prevent end-organ damage. Follow-up of MGUS should be lifelong; however, a risk-adapted approach involving the primary care setting is recommended.