Lymphoplasmacytic Lymphoma/Waldenstrom Macroglobulinemia Masquerading as IgM Warm Antibody Autoimmune Hemolytic Anemia in Association With Mycoplasma pneumoniae Infection: A Case Report

Warm antibody autoimmune hemolytic anemia (AIHA) is mostly of IgG subtype. IgM subtype is extremely rare and has not been reported in association with lymphoplasmacytic lymphoma (LPL)/Waldenström macroglobulinemia (WM). We are reporting the case of a 75-year-old female patient who presented with severe hemolytic anemia and Mycoplasma pneumoniae pneumonia (MPP). Cold agglutinin and serum protein electrophoresis (SPEP) were negative but immunofixation was positive for IgM. Ultimately, hemolytic anemia was labeled warm antibody AIHA in association with MPP. She presented again one year later with more severe hemolytic anemia. Persistently elevated IgM was seen in immunofixation and triggered bone marrow biopsy that confirmed LPL/WM. This case highlights the clinical pearl that warm antibody AIHA in association with MPP is a rare entity and more intensive investigation to rule out other etiologies is mandated. Also, this case is rare as it is of IgM subtype warm AIHA and observed in the context of LPL/WM.