Case Report of IgM Multiple Myeloma: Diagnosing a Rare Hematologic Entity.

IgM multiple myeloma is an exceedingly rare hematologic entity comprising only less than 0.5% of multiple myeloma cases. Given the rarity of this disorder, it makes it a challenge to differentiate from other more prevalent hematologic disorders like Waldenstrom macroglobulinemia. These 2 diseases have the common finding of an IgM monoclonal gammopathy and distinguishing between these 2 diagnoses is of great importance given that therapy and prognosis differ significantly. This report illustrates the case of a 64-year-old man who presented with IgM lambda monoclonal gammopathy in whom signs, symptoms, laboratories, and imaging were initially thought to be consistent with Waldenstrom macroglobulinemia. Upon further analysis, which included bone marrow biopsy, flow cytometry, immunohistochemistry, fluorescence in situ hybridization, and MYD88 (L265P) gene mutation analysis, the rare diagnosis of IgM multiple myeloma was confirmed. As highlighted by this patient's case, reaching the diagnosis of IgM multiple myeloma can be a difficult task which requires a high index of suspicion and accurate diagnostic methods. By using the approach detailed in this report, more cases of IgM multiple myeloma can be diagnosed early, which in turn may lead to earlier treatment and better outcomes.