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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:

Precursors of Myeloma Description

MGUS

  • Benign condition where M-protein (or paraprotein) is present, but there is no underlying disease (ie, no anemia, renal failure, excessive calcium in the blood or bone lesions)
  • Although there may be more abnormal plasma cells than usual in the bone marrow, they account for less than 10% of blood cells
  • Approximately 3.2% of the general population 50 years of age and older have MGUS. Of those, about 1% per year will develop active myeloma.
  • MGUS is usually monitored but not treated

Smouldering Myeloma

  • Transitional state between MGUS and active/symptomatic myeloma
  • M-protein is present in the blood and/or urine
  • Abnormal plasma cells in the bone marrow may account for 10-59% of blood cells
  • Still no symptoms or organ damage
  • Usually monitored but not treated
  • Supportive care may be given

Plasmacytomas

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.

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ADDITIONAL EDUCATIONAL RESOURCES