There are different types of myeloma, and classifications are made by the activity of the disease, as well as by the types of immunoglobulin proteins that are being abnormally produced.
Asymptomatic myeloma, also called smoldering or indolent myeloma, is a slowly progressing/early form of the disease. Although there is an increased level of plasma cells in the marrow and/or an elevated M-protein, there is still no anemia or damage to the bones or kidneys.
One particular type of asymptomatic myeloma -- monoclonal gammopathy of undetermined significance (MGUS) -- produces low antibody levels, but no symptoms or problems. It can develop into active myeloma, but when it does, it does so at a very slow rate. Not everyone with MGUS will go on to develop myeloma, but some may, which is why annual monitoring is necessary.
Because there are few signs of active disease, asymptomatic myeloma is usually monitored, but does not require treatment.
Symptomatic, or active myeloma is characterized by an elevation of plasma cells in the marrow, M- protein detected in the blood or urine, and resulting organ damage. In some cases of symptomatic myeloma, the cancerous cells will collect in a single bone and form a tumor called a plasmacytoma.
Symptomatic myelomas are further classified by the types of immunoglobulin proteins in the blood. Immunoglobulins are named by the type of heavy chain they contain (G, A, M, D, or E).
- The most common M- protein in myeloma is the the IgG type.
- Less common are IgA immunoglobulin myelomas.
- IgD and IgE myelomas are extremely unusual.
- Overproduction of IgM is a rare condition called Waldenstrom's macroglobulinemia.
Some types of myelomas produce an incomplete immunoglobulin of light chains only. These are called light chain myelomas. Light chain proteins are also referred to as Bence- Jones proteins. When Bence-Jones proteins are in the urine, they accumulate in the kidneys and cause damage.
There also some rare diseases in which the cancerous cells overproduce heavy chains only. These are called heavy chain disease and may or may not share characteristics with myeloma. Approximately 1% of myelomas are called non- secretory myeloma. In these patients, the production of M- proteins or light chains is not enough to be detected in the blood or urine. Special testing is required to identify disease in these patients.
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