Acquired Hemophilia A Revealing Occult Splenic Marginal Zone Lymphoma.

BACKGROUND Acquired hemophilia A is a rare autoimmune bleeding disorder caused by inhibitory autoantibodies against coagulation factor VIII and is associated with significant morbidity and mortality. Although malignancy-associated acquired hemophilia A is well recognized, its presentation as the initial manifestation of an otherwise clinically subtle indolent B-cell lymphoma, such as splenic marginal zone lymphoma, remains exceedingly uncommon. We report a case highlighting the importance of recognizing acquired factor VIII inhibitors, evaluating for underlying lymphoproliferative disorders, and the potential role of rituximab monotherapy in achieving control of both the inhibitor and the underlying lymphoma. CASE REPORT A 77-year-old man presented with spontaneous bruising and an isolated prolonged activated partial thromboplastin time that failed to correct on mixing studies. Further evaluation demonstrated markedly reduced factor VIII activity, a factor VIII inhibitor, diffuse splenomegaly, and flow cytometry and bone marrow biopsy findings most consistent with splenic marginal zone lymphoma. Treatment with activated prothrombin complex concentrate, corticosteroids, and rituximab resulted in normalization of coagulation parameters, recovery of factor VIII activity, decline in inhibitor titers, resolution of bleeding manifestations, and sustained clinical stability without recurrent bleeding or evidence of lymphoma progression. CONCLUSIONS This case highlights acquired hemophilia A as a rare paraneoplastic manifestation of splenic marginal zone lymphoma and emphasizes the importance of evaluating for an underlying lymphoproliferative disorder in older adults presenting with newly identified factor VIII inhibitors, particularly in the setting of cytopenias or splenomegaly. It also demonstrates that rituximab-based therapy can effectively achieve sustained remission of both the inhibitor and the underlying indolent lymphoma.