Membrane autoantibodies in systemic lupus erythematosus: a case of autoimmune hemolytic anemia, antiphospholipid antibodies, and transient acquired activated protein C resistance

BACKGROUND: Warm autoimmune hemolytic anemia and antiphospholipid antibodies (which include lupus anticoagulants and anticardiolipin [ACL] antibodies) are associated, respectively, with approximately 10 and 40 percent of cases of systemic lupus erythematosus (SLE). This study reports a case of SLE presenting with an unusual constellation of findings that included an immunoglobulin M (IgM) cold autoantibody of high thermal amplitude, high‐titer ACL antibodies, and transient acquir ed activated protein C resistance. CASE REPORT: A previously untransfused, nulligravid 17‐year‐old woman without a significant medical history presented with signs and symptoms of SLE and an extravascular hemolytic anemia. Spontaneous agglutination was noted in blood samples collected for testing. Serologic testing revealed a normal‐titer, high‐thermal‐amplitude IgM red blood cell (RBC) autoantibody but no additional RBC antibodies in the patient's plasma. Additional testing was significant for a high‐titer ACL IgM and a positive test for activated protein C resistance (a screening test for the Factor [F]V Leiden mutation), which prompted initiation of prophylactic anticoagulation. Confirmatory DNA testing for FV Leiden, however, was negative. The patient's symptoms, anemia, RBC autoagglutinins, ACL antibodies, and activated protein C resistance all resolved after 6 weeks of immunosuppression. CONCLUSION: This case illustrates the wide range of clinical and laboratory findings that autoantibodies against cellular membranes may produce. IgM autoagglutinins of high thermal amplitude associated with a significant extravascular hemolytic anemia may be a presenting feature of SLE. Concomitant antiphospholipid antibodies may interfere with partial thromboplastin time–based tests of hypercoagulability such as that for activated protein C resistance.