Spontaneously acquired factor IX inhibitor in a nonhemophiliac child

A 2 1/2-year-old, previously healthy child developed progressive swelling of the left leg and a hematoma of the anterior chest wall associated with a falling hemoglobin concentration, as a result of a spontaneously acquired Factor IX inhibitor. Successful management of her condition required a four-volume exchange transfusion and immunosuppressive therapy consisting of cyclophosphamide for four days and prednisone for one month. A brief review of the literature regarding the occurrence and nature of acquired coagulation factor inhibitors and the role of immunosuppressive therapy is also presented.