A Rare Case of Autoimmune Hemolytic Anemia Caused by Warm-reacting IgM-class Antibodies Associated with Mycoplasma Pneumoniae Infection

Abstract Introduction/Objective Warm autoantibodies are usually IgG-class and/or IgA-class immunoglobulins. may be classified as agglutinins or hemolysins, which may be incomplete or complete, depending on in vitro serology; they almost always bind complement. Autoimmune hemolytic anemia with only warm IgM autoantibodies is extremely rare. Methods A 91-year-old Caucasian male with hypertension presented with non-productive cough for two weeks, associated with shortness of breath and fatigue. He has a paste history of medical history of high degree AV block with sick sinus syndrome and bradycardia. Results He had blood pressure of 111/53 and heart rate of 50. Laboratory investigations showed leukocytes count of 7, Hemoglobin level of 5.6 g/dl, hematocrit level of 15.5%, platelets count of 267, total bilirubin of 5.6 mg/dL, direct bilirubin of 0.7 mg/dL, and lactate dehydrogenase (LDH) of 372 U/L and IgM titer for Mycoplasma pneumoniae was 1493 units/mL (Ref < 770). He was transfused four units of packed red blood cells as emergency release due to a positive antibody screen. His hemoglobin level increased from 5.6 g/dL to 7.2 g/dL then it decreased from 8.2 g/dL to 5.6 g/dL the next two days. Direct antiglobulin test was 3+ positive for C3d and Negative for IgG. He finished a 7-day course of antibiotic treatment. The results the Cold-agglutinin titer and thermal amplitude test were suggestive of an IgM warm autoantibody and a cold agglutinin of a moderate titer. The results exclude a diagnosis of cold agglutinin syndrome. Conclusion Mycoplasma pneumonia is mainly associated with cold agglutinin syndrome but it is very rare to be associated with WAIHA. WAIHA with a DAT positive for C3 only is relatively rare with an incidence ranging between 6% and 13% and can have a clinical picture ranging from mild to severe anemia. Severe symptomatic hemolysis can be treated with Rituximab, cytotoxic agents or plasmapheresis.