Mayo Clinic – Monoclonal gammopathy of undetermined significance (MGUS)
Monoclonal gammopathy of undetermined significance (MGUS) is a condition that is characterised by the production of an aberrant antibody called M-protein by plasma cells. Similar to multiple myeloma, MGUS is characterised by an increase in M-protein antibodies, as well as the plasma cells that produce them. This increase is lower than that seen in multiple myeloma, however, although approximately 1-2% of MGUS cases ‘evolve’ into multiple myeloma every year. MGUS rarely causes symptoms and is often discovered by accident, such as during a routine blood test.
Within the bone marrow, all blood cells originate from stem cells. This includes white blood cells, such as B-lymphocytes and T-lymphocytes. Forming part of the immune system, these cells respond to foreign invaders of the body, such as bacteria and viruses. When a foreign substance is detected, B-lymphocytes will develop into plasma cells, which produce antibodies that will bind to the foreign substance in an effort to destroy it. These agents are necessary to fight infections and diseases. When an abnormal plasma cell multiplies uncontrollably, the production of the antibody that it produces also increases. This is known as monoclonal gammopathy.
MGUS may occur at any age, but the incidence increases as age progresses. The occurrence of MGUS at the age of 70 is about 5% and increases to 10% at the age of 90. It is just as common in men as in women. In approximately 1% of the MGUS-patients, the disease develops into multiple myeloma. All patients with multiple myeloma have experienced stages of MGUS.
Patients with MGUS hardly experience symptoms and as a result, the disease is usually discovered by accident. The disease may lead to symptoms of decrease in sensation and movement of limbs when the abnormal proteins are directed against the nerves, known as neuropathy. Furthermore, the (abnormal) M-protein can be folded incorrectly, resulting in the protein no longer being soluble in the patient’s blood, causing it to accumulate in tissues and organs as amyloid deposits. This creates the syndrome called amyloidosis.
As with multiple myeloma, the cause of MGUS remains unknown.
MGUS often discovered by accident during routine blood tests. The diagnosis of MGUS is confirmed by, a serum electrophoresis test. During this test the abnormally high quantities of one specific antibody (IgM) or the M-protein can be measured. When there is doubt, additional tests can be carried out, such as bone marrow examination, scans and skeletal photos, to rule out lymphoma or myeloma.
MGUS usually causes no symptoms and does not require treatment. However, due to the risk of developing multiple myeloma, it is important to keep track of these patients. Commonly, a patient with MGUS will be invited for an annual blood test to monitor the increase in M-protein content over time.
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