IgM myeloma (IgM MM) is a unique, rare subtype of multiple myeloma (MM) comprising just 0.5 % of all cases of MM. Like other types of myeloma with monoclonal gammopathies of other immunoglobulins (e.g., IgG, IgA), patients with IgM MM often have classic symptoms including hypercalcemia, anemia, renal failure, and lytic bone lesions (“CRAB” symptoms). However, unlike the other types of MM, IgM MM shares the finding of an IgM monoclonal gammopathy with another hematologic process, Waldenstrom’s macroglobulinemia (WM). Clinicians are presented with a diagnostic dilemma when a patient presents with a variety of concerning symptoms and an IgM monoclonal gammopathy. Distinguishing these two diagnoses is critical as the approach to therapy and prognosis greatly differ [1, 2]. This chapter intends to summarize recent literature that help define IgM MM, highlight clinical features of this rare subtype, and review treatment considerations for this rare disease.
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