ISSN 2997-1036
International Journal of Hematology | Vol. 17, No. 7, July 2026 | pp. 49–56
DOI: 10.46882/2026/IJH/000197
Case Report
Title: Spontaneous massive retroperitoneal hemorrhage secondary to acquired Factor XI inhibitor development in an elderly patient: Eradication with azathioprine and methylprednisolone
Names of Authors: K. L. Musa¹, M. N. Lawal², O. P. Dikko³
Authors’ Affiliations: ¹Department of Haematology, Federal Medical Centre, Katsina, Nigeria; ²Department of Surgery, Bayero University, Kano, Nigeria; ³Department of Pathology, Ahmavu Bello University Teaching Hospital, Zaria, Nigeria
Abstract: Spontaneous development of neutralizing autoantibodies directed against contact activation pathway components is an exceptionally rare clinical condition that causes catastrophic bleeding events in elderly populations. We report a 74-year-old male who presented with sudden, unprovoked left flank pain, lower abdominal distension, and hypovolemic shock. Abdominal computed tomography confirmed a massive retroperitoneal hematoma measuring 12.4 × 8.5 cm without prior trauma or anticoagulant exposure. Coagulation profiles demonstrated isolated, severe prolongation of activated partial thromboplastin time (92.4 seconds) with a normal prothrombin time. A 1:1 mixing study with normal pooled plasma failed to correct the activated partial thromboplastin time, indicating a specific intrinsic pathway inhibitor. Functional assays confirmed severely depressed Factor XI activity (< 1.5%), and a Bethesda assay quantified a Factor XI inhibitor titer of 18.0 Bethesda Units. Hemostasis was achieved using recombinant activated Factor VII bypassing agents (90 μg/kg every 3 hours) alongside supportive measures. Subsequent immunosuppressive therapy with oral methylprednisolone paired with azathioprine (100 mg daily) successfully cleared the inhibitor (0 BU) and normalized Factor XI activity by week 8. This case demonstrates that acquired Factor XI autoantibodies require immediate diagnostic differentiation and multi-modal therapeutic strategies.
Keywords: Acquired factor XI inhibitor, retroperitoneal hemorrhage, intrinsic pathway, bypassing agents, azathioprine
Manuscript Timeline: Received: April 18, 2026; Revised: May 22, 2026; Accepted: June 10, 2026; Published: July 16, 2026