A Case of Acquired Factor V Inhibitor During Bullous Pemphigoid Treatment.

Acquired factor V inhibitor (AFVI) is a rare coagulation disorder caused by the production of anti-factor V antibodies in response to infection, surgery, malignancy, autoimmune disease, antibiotics, or other drugs. Its clinical manifestations vary from asymptomatic to severe; hence, optimal treatment is difficult. Bullous pemphigoid (BP) is an autoimmune disorder caused by autoantibodies against dermal-epidermal junction structural proteins. We describe a patient with BP and AFVI, successfully treated with prednisolone. A 78-year-old Japanese man presented with tense hemorrhagic blisters on his trunk and extremities. Owing to his urinary tract infection and advanced age, oral prednisolone was initiated at 20 mg (0.3 mg/kg/day) for BP. Three weeks after treatment, upper gastrointestinal bleeding, hemorrhagic shock, aspiration pneumonia, and hematuria occurred. An elevated anti-BP180 antibody titer (2050 U/mL) indicated BP, and a prolonged activated partial thromboplastin time (aPTT, >180 seconds) indicated a coagulation disorder; the international normalized ratio was too prolonged to be calculated. Based on low factor V activity (<1%) and an inhibitor pattern in an aPTT cross-mixing test, we diagnosed possible AFVI. Despite BP and AFVI stabilization, prednisolone administration (18 mg/day), and normal aPTT, the patient died of septic shock due to cholangitis. In conclusion, clotting-related tests, including factor V tests, should be performed if coagulation disorders persist during the treatment of autoimmune diseases such as BP. There is a hypothesis that immunoglobulin G4 is associated with AFVI and BP and that there is a homologous sequence between factors Ⅷ and V and the BP180 protein. This may explain the immediate resolution of the disease after prednisolone administration.