Myeloma, affecting the bone marrow, is a cancer of blood plasma cells. Plasma cells are derived from mature B lymphocytes, which are a type of white blood cell. These cells render immunity to the body by producing immunoglobulins or antibodies in response to foreign bodies, such as bacteria or viruses. Plasma cells only constitute about 2-3% of all the cells in the bone marrow, but in myeloma they proliferate and make up about 10% of all the cells in the bone marrow. Since, their function is to make antibodies, when there is abnormal proliferation of plasma cells; there is excessive production of abnormal myeloma protein (M-protein) in the form of IgG, IgA, IgM and light chains. In addition, there is end organ damage including, anemia (normochromic, normocytic with Hb <10 g/dl or Hb value >2 g/dl below the lower limit of normal), hypercalcemia (serum calcium ≥11.5 mg/dl), bone lesions (lytic lesions, severe osteopenia or pathologic fractures) and renal insufficiency (serum creatinine >1.73 mmol/l).
Is Myeloma And Multiple Myeloma The Same?
Since, bone marrow is found in multiple bones of the body, myeloma is also found in different parts of the body where bone and bone marrow is affected, thus the name multiple myeloma. Thus, myeloma and multiple myeloma may be considered as the same entity.
Bone marrow is the soft and spongy tissue found in the hollow spaces of bones. They are mostly found in flat bones, including hip bones, sternum, skull, ribs, vertebrae, shoulder blades, and metaphyseal and epiphyseal ends of long bones, such as femur, tibia, and humerus. Therefore, myeloma can occur in all these sites, but more common sites are ribs, sternum, vertebrae, skull and pelvis. (1)
Myeloma falls under the spectrum of diseases known as plasma cell dyscrasias and it needs to be differentiated from other plasma cell disorders. The other diseases and differentiating criteria include:
MGUS (Monoclonal Gammopathy Of Undetermined Significance)- It should have serum monoclonal protein <3 g/dl with clonal bone marrow plasma cells <10% and absence of end organ damage such as hypercalcemia, anemia, bone lesions and renal insufficiency. (2)
Smoldering Multiple Myeloma Or Asymptomatic Multiple Myeloma- It should have serum monoclonal protein ≥3 g/dl and/or clonal bone marrow plasma cells ≥10%, in addition to absence of end organ damage. (3)
Solitary Plasmacytoma- It should be positive for biopsy proven solitary lesion of bone or soft tissue with presence of plasma cells, normal bone marrow with no evidence of clonal plasma cells, normal skeletal survey and MRI of spine and pelvis (except for the primary solitary lesion) and absence of end organ damage (CRAB criteria).
Waldenstrom’s Macroglobulinemia- In this, there is IgM monoclonal gammopathy (regardless of the size of M protein) and >10% of bone marrow lymphoplasmacytic infiltration by small lymphocytes, exhibiting plasmacytoid or plasma cell differentiation and immunophenotype that excludes other lymphoproliferative disorders (chronic lymphocytic leukemia and mantle cell lymphoma).
Systemic AL Amyloidosis- It includes the presence of amyloid related systemic syndrome (involvement of heart, liver, kidneys, GI tract or peripheral nerves), positive amyloid staining by Congo red in tissues, evidence of light chained amyloid and evidence of monoclonal plasma cell proliferative disorder.
POEMS Syndrome– In this, there is presence of monoclonal plasma cells, peripheral neuropathy and at least one of the following seven features, which include, osteosclerotic bone lesions, organomegaly, Castleman’s disease, endocrinopathy (except diabetes mellitus or hypothyroidism), edema, papilledema and skin changes. The common features of the syndrome include elevated plasma or serum levels of vascular endothelial growth factor and thrombocytosis.
Multiple myeloma evolves from a pre-malignant condition known as MGUS. MGUS is prevalent in approximately 3% of all adult population over 50 years of age and progresses to myeloma in about 1% people every year. In some individuals, it is also preceded by more advanced pre-malignant condition known as asymptomatic multiple myeloma or smoldering multiple myeloma. Although, there are advances in the treatment of myeloma and patients prognosis have improved in the last decade, there is still no permanent cure for the disease.
- Rajkumar SV. Multiple myeloma. Curr Probl Cancer. 2009;33(1):7–64. doi:10.1016/j.currproblcancer.2009.01.001
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