The Unexpected Clot: Unilateral Brachial Artery Occlusion Unmasking Antithrombin III Deficiency; Case Report and Therapeutic Considerations

Antithrombin III deficiency is an autosomal dominant thrombophilia that most commonly predisposes carriers to venous thromboembolism but can rarely cause arterial thrombosis, particularly when quantitative or qualitative defects are severe.A 46-year-old woman on combined oral contraceptive therapy presented with recurrent acute upper-extremity arterial occlusions. Workup revealed hereditary antithrombin III deficiency. She underwent emergency embolectomy with initial issues of anticoagulation and was then converted to a direct oral anticoagulant with clinical stabilizationPeri-procedural heparin responsiveness was suboptimal due to low antithrombin activity and was managed with surgical embolectomy followed by later anticoagulation with a direct oral factor Xa inhibitor. Direct oral anticoagulants have been suggested as alternative therapies in antithrombin-refractory patients, and replacement with antithrombin concentrate can reversibly correct heparin responsiveness when employed judiciously. The patient was counseled to stop estrogen-containing medications, manage modifiable risk factors, and have vascular longitudinal surveillance.It is a new presentation of arterial thrombosis with antithrombin III deficiency caused by exogenous estrogen exposure that was effectively treated with embolectomy and prolonged direct oral anticoagulation. Identification of this phenotype guides the secondary prevention and family screening in hereditary thrombophilia.