Background: Acquired Hemophilia A (AHA) is a rare autoimmune bleeding disorder where autoantibodies are directed against clotting factors, most commonly factor VIII. The etiology is poorly understood but it is most commonly associated with pregnancy/postpartum status, malignancy and other autoimmune disorders.

Aims: Case Presentation.

Methods: Our patient is an 84-year-old female with a history of hypertension (HTN), hyperlipidemia (HLD) and left total hip arthroplasty (THA), who presented with progressively worsening pain and bruising to her left posterolateral thigh of 5 weeks duration. Her laboratory studies were significant for Partial Thromboplastin Time (PTT) of 80, hemoglobin of 5.7, platelet count of 650,000 and C reactive protein of 6.3. Computed Tomography of the Pelvis and lower extremity revealed multiple low-attenuation, large hematomas (range: 7-8 cm), which were evidently expanding muscle groups of the posterior thigh, triggering concerns for compartment syndrome.

Results:

The workup for the elevated PTT resulted in a positive mixing study, a low factor VIII assay, and an elevated factor VIII inhibitor level using the Bethesda assay. A clinical diagnosis of Acquired Autoimmune Hemophilia A was established. Treatment was then initiated with low-dose corticosteroids and Cyclophosphamide. Factor VIII inhibitor levels peaked at 124 Bethesda Units (BU). Subsequently, Rituximab was added due to first-line treatment refractoriness. Factor VIII inhibitor levels then decreased to 24 BU and continued to downtrend. 

Factor 8 Activity vs. Inhibitor Levels Throughout Admission

Conclusions: Diagnostic Algorithm of Acquired Hemophilia A
Acquired hemophilia A is a rare autoimmune disorder with uncertain etiology. One of the major complications resulting from factor VIII assay activity less than 1% is spontaneous hematoma formation. Improvements in Factor VIII assay typically will not be seen until inhibitor levels are below 10 BU. Interestingly, the observed 80% decline in the inhibitor level occurred after only one dose of Rituximab, suggesting a possible synergistic effect between Cyclophosphamide and corticosteroid. There are currently no definitive guidelines governing treatment of AHA.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/acquired-hemophilia-a-presenting-as-spontaneous-intramuscular-hematomas/