Cryoagglutinin autoimmune hemolytic anemia secondary to Mycoplasma pneumoniae infection in patient with pernicious anemia: A case report.

This report describes the rare case of a patient with autoimmune hemolytic anemia due to cryoagglutinins secondary to Mycoplasma pneumoniae infection, coexisting with pernicious anemia. A 56-year-old man presented with a ten-day history of cough and mucocutaneous pallor. Laboratory studies revealed megaloblastic anemia with low vitamin B12 levels, positive antibodies against intrinsic factor and parietal cells, as well as hemolysis parameters and a positive direct Coombs test for complement (C3d) with cryoagglutinins active at low temperatures. M. pneumoniae infection was confirmed by indirect immunofluorescence for IgM and IgG. Intramuscular B complex supplementation and doxycycline were administered for 14 days, improving hemoglobin and other hematological parameters within four weeks. This case highlights the diagnostic complexity in patients with rare hemolytic anemias in the context of atypical infections and underscores the importance of a multidisciplinary approach for their diagnosis and appropriate treatment. The coexistence of cryoagglutinin-mediated autoimmune hemolytic anemia and pernicious anemia poses diagnostic and therapeutic challenges that are relevant to clinical practice.