Monoclonal gammopathy of undetermined significance (MGUS) is a plasma cell dyscrasia in which plasma cells or other types of antibody-producing cells secrete a myeloma protein, i.e. an abnormal antibody, into the blood; this abnormal protein is usually found during standard laboratory blood or urine tests. It is a type of monoclonal gammopathy. MGUS resembles multiple myeloma and similar diseases, but the levels of antibodies are lower, the number of plasma cells (white blood cells that secrete antibodies) in the bone marrow is lower, and it rarely has symptoms or major problems. However, since MGUS can progress to multiple myeloma, with a rate ranging from 0.5% to 1.5% per year depending on the risk category, yearly monitoring is recommended.
The progression from MGUS to multiple myeloma usually involves several steps. In rare cases, it may also be related with a slowly progressive symmetric distal sensorimotor neuropathy.