Plasma cells produce immunoglobulins (Ig), or antibodies, substances that circulate in the blood to defend the body by attacking any foreign substances that enter the organism. Each Ig has two heavy chains: gamma (IgG), alfa (IgA), mu (IgM), delta (IgD), or epsilon (IgE), and two light chains (kappa or delta).

Monoclonal gammopathies include a group of diseases characterised by the clonal proliferation of plasma cells that produce a single type of light and/or heavy chain (monoclonal component) in excessive quantities.

The term monoclonal gammopathy of undetermined significance (MGUS) is used when a monoclonal component is present but the diagnostic criteria are lacking to diagnose multiple myeloma, primary amyloidosis, Waldenström macroglobulinemia or heavy chain disease. Monoclonal gammopathy may also be referred to as idiopathic gammopathy.

MGUS has a considerable prevalence amongst those of advanced age, being observed in 1% of people over the age of 60 and more than 5% in those over 80 years of age.

In most cases (60-70%) MGUS is detected by chance as a result of a routine blood test.

Diagnosis is based on the presence of monoclonal immunoglobulins in quantities lower than 30 g/L and a percentage of bone marrow plasma cells lower than 10%, with the absence of organic injury attributable to the gammopathy (renal, bone, etc.).

All MGUS patients must be monitored and undergo regular checks. It is important to establish the differential diagnosis between MGUS and multiple myeloma since MGUS does not require treatment, whereas multiple myeloma generally does.

According to various studies, 12%, 25% and 30% of MGUS patients develop multiple myeloma after 10, 20 and 25 years respectively. The only way to establish whether MGUS is really benign, or if it constitutes the first manifestation of multiple myeloma is to undertake an annual test of the M component (anomalous monoclonal antibody).

For more quality information about MGUS, you can consult the following websites:

• Plasma cell neoplasms treatment. National Cancer Institute.
• Monoclonal Gammopathy of Undetermined Significance (MGUS). Leukemia and Lymphoma Society.