Types and Precursors of Myeloma
Myeloma is really not just one disease. It's a disease with several subtypes. In myeloma, abnormal plasma cells (myeloma cells) produce an unusually high number of only one of the types of antibodies – or immunoglobulins, as doctors often call them. The specific type of immunoglobulin that is overproduced by myeloma cells can vary from one person to the next, and determines the subtype of myeloma that the patient has.
When plasma cells are exposed to foreign substances (antigens), they produce different antibodies called immunoglobulins. Immunoglobulins are made up of two types of protein:
- Heavy chains (A, G, M, D and E)
- Light chains (kappa [κ] or lambda [λ])
About 60-65% of all cases of myeloma involves the overproduction of immunoglobulins (Ig) made with "G" heavy chains (IgG). When too much of the same immunoglobulin is produced, this is referred to as monoclonoal protein (M-protein), monoclonal spike (M-spike), monoclonal peak (M-peak) or paraprotein.
Precursors of Myeloma
Monoclonal Gammopathy of Undetermined Significance (MGUS) and Smouldering (Asymptomatic) Myeloma
Conditions such as MGUS and smouldering myeloma may be precursors to active (symptomatic) myeloma:
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Sometimes, myeloma cells collect in a single bone and form a tumour called a solitary plasmacytoma of the bone. Occasionally, a plasmacytoma can affect areas of soft tissue outside of the bone and bone marrow (called an extramedullary plasmacytoma). Both types of plasmacytoma are most often treated with radiation therapy; however, the majority of patients with plasmacytoma of the bone eventually progress to active myeloma.
Symptomatic or Active Myeloma
Symptomatic (active) myeloma requires treatment. The International Myeloma Working Group (IMWG) expanded the definition of active myeloma, to include any one of the following "SLiM" criteria to confirm the diagnosis of myeloma:
- Sixty (60) percent or greater abnormal plasma cells on bone marrow examination
- Light chain ratio (free, involved/uninvolved) of 100 or more in the blood (involved must be at least 100 mg/L)
- MRI (magnetic resonance imaging) with more than one bone lesion (5 mm or greater)
Traditionally, the diagnosis of myeloma was based on:
- M-protein is present in the blood or urine
- Abnormal plasma cells account for 10% or more of blood cells in the bone marrow
- Symptoms or complications may include one or more of the following "CRAB" criteria:
- Calcium elevation in the blood
- Renal insufficiency (kidney failure)
- Anemia (low red blood count)
- Bone disease (pain, increased risk of fractures, etc.)
For more information, dowload the Multiple Myeloma Patient Handbook
Designed to provide educational support to patients, caregivers, families and friends, this handbook gives accurate, reliable, and clear information on myeloma. Topics cover its causes and effects, how it is diagnosed and the treatment options available in Canada.