The diagnosis is based on histologic evidence of a tumor consisting of monoclonal plasma cells and the absence of multiple myeloma on the basis of bone marrow, radiographic, and appropriate studies of blood and urine. Complete skeletal radiographs must show no other lesions of multiple myeloma (Table 84.2). If magnetic resonance imaging of the spine and pelvis reveals skeletal lesions, the condition should be classified as smoldering multiple myeloma. Approximately one-fourth to one-third of patients with an apparently solitary plasmacytoma will have abnormalities on magnetic resonance imaging.5-7 These patients are at greater risk for progression to multiple myeloma. Immunofixation of serum and concentrated urine ideally should have no monoclonal (M) protein, but approximately half of the patients do have a small amount of M protein in the serum or urine. This often disappears after tumoricidal radiation. Most patients with solitary plasmacytoma of bone have normal, uninvolved immunoglobulin levels.1 There is no anemia, hypercalcemia, or renal insufficiency that is related to the plasmacytoma. Although the bone marrow aspirate and biopsy must contain no evidence of multiple myeloma, a few plasma cells may be seen.

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