Monoclonal gammopathy of undetermined significance (MGUS)
MGUS is diagnosed when a type of protein, called M protein, is detected in the blood. This protein is made in the bone marrow. Usually, MGUS has no symptoms and no treatment is required. However, patients should be screened regularly as MGUS can develop into more serious conditions. MGUS occurs in about 1% of the general population; in about 1% to 2% of these cases, MGUS develops into myeloma.
A single group of myeloma cells in the bone or soft tissue or a single lesion is called a solitary or isolated plasmacytoma. Solitary plasmacytomas can occur in any bone, but most frequently occur in the bones of the spine.
Solitary plasmacytoma can be detected by X-ray imaging, positron-emission tomography scan, or magnetic resonance imaging. The malignant cells are then identified via biopsy where a needle is inserted into the bone or soft tissue to collect a sample of the cells, which can then be tested. Blood test results and kidney function are usually normal in these patients.
Solitary plasmacytoma is very rare, found in about 5% of plasma cell diseases. It is treated with radiation therapy and usually does not require surgery. Although the prognosis is good, solitary plasmacytoma may return and progress to myeloma. Patients should, therefore, be screened regularly following treatment.
Smoldering multiple myeloma (SMM)
SMM is diagnosed by the detection of low levels of M protein in the blood and an increased number of abnormal cells in the bone marrow. Patients may also have several small lesions in their bones.
Many — but not all — SMM patients progress to myeloma. About 10% of SMM patients develop myeloma each year in the first five years after diagnosis. Between five and 10 years after diagnosis, the risk drops to about 3% and is roughly 1% in subsequent years.
The treatment for SMM has previously been “watchful waiting,” but studies are showing that treating patients before symptoms appear may slow down the progression to cancer, especially in those who are genetically predisposed to myeloma.
Myeloma is the result of the abnormal growth and division of a type of white blood cell called B-cells. Because it usually affects several bone marrow sites, the disease is also known as multiple myeloma.
More than 90% of patients have multiple lesions at the time of diagnosis. Patients also have increased levels of M protein and abnormal plasma cells or activated B-cells in the blood. These abnormal plasma cells may also be present in the urine.
Last updated: Feb. 27, 2020
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