RESUMO
Acquired haemophilia is a rare disease; it occurs most frequently in elderly patients. The majority of cases are due to autoantibodies to factor VIII, which deplete circulating factor VIII or acquired haemophilia A. Only few cases of acquired haemophilia B are reported until today. We report a case of a 7-year-old girl with no past medical history of bleeding disorder and who present an extensive haematoma in the left calf. The diagnosis was established by the demonstration of an isolated prolongation of the activated partial thromboplastin time (APTT) with a reduced factor IX level and evidence of factor IX inhibitor activity to 2 Bethesda Unit (2UB). Diagnosis of acquired haemophilia B confirmed, patient received recombinant factor VIIa and corticosteroid treatment. Bleeding symptoms had completely disappeared and coagulation tests become normal. In conclusion, if bleeding symptoms are associated with unexplained prolongation of APTT, an inhibitor against factor must be searched for not missing an acquired coagulation disease.