Characterization of anti-factor VIII antibody in a patient with acquired hemophilia A
A 67-year-old female, experiencing 12 h of acute abdominal and right flank pain, was admitted to our hospital through the emergency department. Her medical history was unremarkable, except for hypertension controlled with amlodipine. The patient had no family history of abnormal bleeding. One week prior to hospital admittance, she developed bruises on her left lower extremity and gross hematuria. She did not receive medical care, and these conditions resolved spontaneously.\nInitial examination revealed pale conjunctiva and both soft-tissue swelling and bruising on her left lower extremity. Tenderness to palpation over the lower abdomen and rebound tenderness were noted. Her vital signs were within normal ranges. Complete blood cell count indicated hypochromic anemia with normal white blood cell counts (hemoglobin, 8.2 g/dL; hematocrit, 23.9%; white blood cell counts, 9.1×109/L; platelet counts, 342×109/L). The patient's prothrombin time (PT, 12.5 s; international normalized ratio [INR], 1.11) and thrombin time (TT, 14.3 s) were normal. Her activated partial thromboplastin time (APTT, 77.4 s) was prolonged and not corrected by incubation mixing test (APTT, 68.2 s).\nAbdominal computed tomography scan demonstrated multifocal fluid collections throughout the abdomen and pelvis, localized mainly on the right side. An enlarged psoas muscle, intramuscular hematomas in the right iliopsoas, and a paravertebral muscle with active bleeding were noted. Multiple calcifications within the pancreas and atrophy of the pancreatic parenchyma suggested chronic pancreatitis. The spleen, liver, and gall bladder appeared normal. Angiography of the abdominal arteries demonstrated suspicious extravasation from a right lumbar artery. Gelfoam embolization of the right second and third lumbar arteries was performed. The patient was immediately treated with recombinant FVIIa (90 IU/kg every 6 to 8 h; NovoSeven) for 2 days because of active bleeding. The FVIII level was 2%, and the titer of FVIII inhibitor was 14.6 Bethesda units (BU)/mL. The levels of FIX (121%), FXI (90%), and FXII (94%) were all within normal ranges. The patient was treated with oral prednisolone (30 mg/d) and azathioprine (150 mg/d) to eradicate the autoantibody. The tests for anti-nuclear antibody, lupus anticoagulant, hepatitis B virus surface antigen, hepatitis C virus antibody, and human immunodeficiency virus antigen and antibody were all negative, with the exception of anti-Ro antibody (3+). After 2 days of immunosuppressive treatment, the patient's flank pain and hematuria resolved and, 2 weeks later, the hematoma disappeared. On the 45th hospital day, the patient was discharged on oral prednisolone (20 mg/d) and azathioprine (150 mg/d), without further complications. The prednisolone treatment was discontinued approximately 6 months later. The patient's APTT normalized; her FVIII level reached the upper 50%, and the inhibitor was undetectable ().\nAPTT waveform analysis (MDA series; Organon, Technika) of the patient's plasma showed a delayed clotting pattern compared to normal pooled plasma (). Thrombin generation assay (Thermo Fisher Scientific, Waltham, MA, USA) showed decreased production of thrombin in the patient's plasma compared to normal plasma. Virtually no hemostatic effect occurred after the infusion of plasma. Slight improvement in the waveform analysis, but not in the thrombin generation test, was noted (not shown). Enzyme-linked immunosorbent assay demonstrated that the patient's antibody belonged to the immunoglobulin (Ig) G4 subclass. Immunoblotting assays demonstrated that the light chain (A3/C1/C2 domain) of FVIII is the binding region of the autoantibody (, ).