Emicizumab for acquired haemophilia A: A case series.

Background: Emicizumab is approved to prevent bleeding in patients with congenital haemophilia A with or without inhibitors. However, no randomized trials addressed the efficacy of emicizumab in acquired haemophilia A (AHA).

Aims: To report the clinical and biochemical response of emicizumab in AHA.

Methods: This single-centre retrospective study included seven adults with AHA between November 2020 and May 2022. We collected patient characteristics, laboratory coagulation parameters, the use of haemostatic agents, bleeds and thrombotic events. Treatment was monitored using chromogenic FVIII assays. The assay with human reagents assesses both the emicizumab FVIII-like-activity and native patient FVIII-activity. The assay with bovine reagents only measures the patients' native FVIII-activity as emicizumab does not bind to bovine reagents.

Results: Patients presented with spontaneous hematoma (n = 7), intramuscular bleeding (n = 2), haematuria (n = 2) and/or gastro-intestinal bleeding (n = 2). Six patients had major bleedings. At diagnosis, APTT was prolonged (91 seconds, IQR 73-103), FVIII activity was 0% (IQR 0-1) and FVIII inhibitor 182 BU/mL (IQR 104-228). Emicizumab was administered weekly (3 mg/kg) for 4 weeks, and thereafter every 2 weeks until regression of the inhibitor. Three patients received activated FVIIa (cumulative dose of 1.7 mg/kg, IQR 1.2-2.2). All bleedings were controlled after treatment initiation, without further bleeds. After starting emicizumab, FVIII-like activity reached ≥5% at 12 days (IQR 7-14), whereas recovery of the intrinsic FVIII-activity ≥5% occurred at 128 days (IQR 88-173), coinciding with the disappearance of the FVIII inhibitor. There were no safety issues.

Conclusion: In this AHA case series, no new clinically relevant bleeds were observed after initiation of emicizumab in conjunction with standard immunosuppressive therapy.