Background: Development of FVIII inhibitors represents a major challenge in patients with mild haemophilia A (HA), because they tend to occur at an older age and classical immune tolerance induction appears to be less effective.
Case report: A man (age: 60 years) with mild HA due to the missense mutation, Leu1929Arg, received a single dose of rFVIII at 35 IU/kg prior to routine colonoscopy, totalling 25 lifetime exposure days. Two months later, rFVIII was infused for a traumatic hip haematoma. However, FVIII recovery was inappropriate, and a FVIII inhibitor of 19 BU with type-2 kinetics was detected, resulting in FVIII:C of <1%. Two weeks later, the patient experienced spontaneous iliopsoas bleeding. Parallel to bypassing therapy, we started single-agent immunosuppression with prednisolone at 1.5mg/kg. FVIII:C "normalized" at 10.2% after four weeks. After five months, the inhibitor titre fell to <0.4 BU with sustained remission after one year of follow-up.
Conclusion: In mild HA, FVIII inhibitors may share characteristic features with FVIII autoantibodies commonly observed in acquired HA. Therefore, immunosuppressive therapy alone could be successful at least in a subset of patients.