What is multiple myeloma?

Updated: Mar 15, 2019
  • Author: Michael E Mulligan, MD; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Multiple myeloma is the most common primary malignant neoplasm of the skeletal system. The disease is a malignancy of plasma cells. Clinical definitions of the various myeloma subtypes have been updated, as have the imaging definitions of what constitutes bone marrow disease and individual bony involvement. [1] The etiology of multiple myeloma is the monoclonal proliferation of plasma B cells, with resultant marrow infiltration and increase of a single immunoglobulin and its fragments in the serum and urine. Electrophoretic analysis shows increased levels of immunoglobulins in the blood as well as light chains (Bence-Jones protein) in the urine. Radiologically, multiple destructive lytic lesions of the skeleton, as well as severe demineralization, characterize multiple myeloma. A focal lytic lesion must be 5 mm or greater in size to be considered a true abnormality by the latest International Myeloma Working Group (IMWG) criteria. [1, 2]

The marrow infiltration process may involve any bone, but the predominant sites include the vertebral column, ribs, skull, pelvis, and femora. Although the osseous structures may appear radiographically normal or simply osteopenic, the classic appearance is of multiple, discrete, small, lytic lesions. Occasionally, a single lytic lesion is discovered and is termed a plasmacytoma (solitary myeloma). Patients with a single focus of disease often progress to multiple sites of myelomatous involvement. [1, 3, 4, 5, 6, 7]

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