A 15-year-old female was admitted to our hospital because had noticed small purpura on her arms and her legs during 2 weeks before the admission. At the same time, she started having headaches, polyarthritis, and shortness of breath on exertion. These symptoms progressively deteriorated, thus prompting her hospital visit. On her physical examination, body temperature was 38.2°C. Her consciousness was alert. Small purpura were scattered over her entire arms and legs. A malar rash was also recognized on her face. Broad spectrum antibiotic (doripenem hydrate, 1.5 g/day) was involved in the initial therapy because severe bacterial infection was suspected in the situation with undetermined diagnosis on the admission. However, bacterial cultures from her blood, urine, sputum, and throat swab revealed no signs of any bacterial infections and we subsequently excluded bacterial infection from the diagnosis. Titers of antibodies against various kinds of virus such as cytomegalovirus, Epstein-Barr virus, and parvovirus B19 were also negative. Laboratory findings : The serum hemoglobin level was low at 6.4 g/dL (normal range; 12.0–16.0 g/dL), her platelet count was also low at 4000/μL (normal range; 15.0-35.0×104/μL). The number of white blood cells was within normal range. Although the serum levels of fibrinogen degradation products (FDP) and D-dimers were elevated to 17.4 μg/dL (normal range; less than 5.0 μg/dL) and 8.78 μg/dL (normal range; less than 2.0 μg/dL), respectively, the serum level of fibrinogen, prothrombin time (PT), and activated partial thromboplastin time (aPTT) were normal. The serum level of lactate dehydrogenase (LDH) was elevated to 915 IU/L (normal range; 119–219 IU/L), and that of total bilirubin level was also elevated at 2.9 mg/dL (normal range; 0.2–1.3 mg/dL) with dominant elevation of indirect bilirubin. The blood urea nitrogen (BUN) and creatinine levels were within the normal range and urinalysis did not show any abnormal findings. Although her serum haptoglobin levels were decreased at less than 10 mg/dL (normal range; >43–180), both the direct and indirect Coombs tests were negative. The patient’s bone marrow cells obtained by aspiration revealed normal differentiation, however, a peripheral blood smear test clearly showed schistocytes in the RBC. Her antinuclear antibody (ANA) test was positive, and she also had anti-DNA antibodies, anti-SS-A antibodies, anti-RNP antibodies, and anticardiolipin antibodies. Her serum complement levels were decreased (CH50; 21U/mL, C3; 81 mg/dL, and C4; 8 mg/dL, normal range; CH50 32–49 U/mL, C3 65–135 mg/dL, C4 13–35 mg/dL, resp.) and increased immune complex formation was observed (ICc1q 3.3 μg/mL, normal range; 0–3.0 μg/mL). She has positive for ANA, anti-DNA antibody, anti-cardiolipin antibody.
What is the most likely diagnosis? Comente el caso