The unexpected clot: unilateral brachial artery occlusion unmasking antithrombin III deficiency; case report and therapeutic considerations

BACKGROUND: Antithrombin III (AT III) deficiency is a rare autosomal dominant thrombophilia that typically predisposes carriers to venous thromboembolism. Arterial thrombosis is uncommon but may occur in severe quantitative or qualitative defects, particularly when compounded by exogenous risk factors such as estrogen exposure. CASE PRESENTATION: We report a 47-year-old woman on combined oral contraceptives who presented with acute left upper-extremity ischemia due to complete brachial artery occlusion. Emergency embolectomy was performed, but early re-thrombosis occurred. Laboratory studies showed reduced levels of antithrombin III confirmed by immunoradiometric testing, otherwise unremarkable in terms of thrombophilia and autoimmune screening. Genetic studies showed homozygosity of MTHFR 677T and ACE D.D. genes, both of which were looked upon in the context of this case as coincidental. The patient’s response to heparin therapy remained suboptimal until fresh frozen plasma infusion temporarily corrected antithrombin deficiency. Patient’s condition stabilized with chronic anticoagulation therapy using apixaban. DISCUSSION: This particular case illustrates the diagnosis and treatment difficulties that may be encountered in arterial thrombosis in the context of hereditary antithrombin III deficiency. Cases complicated by resistance to heparin are difficult in terms of anticoagulant therapy in the period preceding procedures, although DOACs are effective in anticoagulation irrespective of antithrombin levels. The triggering role of estrogen in this condition must be recognized in family screening. CONCLUSION: Acute upper-extremity arterial thrombosis can unmask hereditary AT III deficiency, particularly in the setting of estrogen therapy. Early surgical therapy, adjustment of antithrombin levels, and the switches to DOACs are essential in keeping the limbs viable and preventing further occurrences. This particular case illustrates the need to put together the different aspects of biochemistry and medicine in rare cases of thrombophilia.