Acquired inhibitor against factor IX in a child: successful treatment with high-dose immunoglobulin and dexamethasone.

The occurrence of acquired inhibitor against factor IX:C is infrequent in haemophilia B patients and is very rare in previously healthy subjects, in whom it is often related to underlying diseases. We describe the case of a 2-year-old girl, who was referred to our hospital with haematomas, without previous bleeding history. Prolonged APTT, normal PT and a factor IX:C level below 1% were found. An inhibitor against factor IX:C was detected (5.5 U mL(-1)). Her father and mother showed normal factor IX:C levels. Treatment with high-dose immunoglobulin (400 mg kg(-1) day(-1) for 5 consecutive days by intravenous infusion) and dexamethasone (4 mg three times a day by intravenous injection for 4 consecutive days) normalized factor IX:C levels and overcame the inhibitor. In conclusion, high-dose immunoglobulin and high-dose dexamethasone are a successful and safe immunosuppressive approach for recovery from inhibitor occurrence.