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Monoclonal Gammopathies of Undetermined Significance (MGUS)

by James R. Berenson, MD

A monoclonal gammopathy of undetermined significance is a buildup of monoclonal antibodies produced by abnormal but noncancerous plasma cells.

In general, monoclonal gammopathies of undetermined significance occur in more than 5% of people older than 70, but they do not cause significant health problems.

These disorders do not usually cause symptoms, so they are almost always discovered by chance when laboratory tests are done for other purposes, such as to measure protein in the blood. However, the monoclonal antibody can bind to nerves and lead to numbness, tingling, and weakness. People with these disorders also are more likely to have bone loss and fractures.

The M-protein levels in people with a monoclonal gammopathy of undetermined significance often remain stable for years—25 years in some people—and do not require treatment. However, if evaluation shows evidence of significant loss of bone density (osteopenia or osteoporosis), doctors may recommend treatment with bisphosphonates.

For unknown reasons, in about one quarter of people with these disorders, there is a progression to a cancer, such as multiple myeloma, macroglobulinemia, or B-cell lymphoma, often after many years. This progression cannot be prevented. About twice a year, people with a monoclonal gammopathy of undetermined significance are usually monitored with a physical examination and blood and sometimes urine tests to determine whether progression to cancer is beginning to occur. If progression is detected early, symptoms and complications of the cancer may be prevented or treated sooner.