Quantitative Antithrombin Deficiency Manifesting as Cerebral Sinus Thrombosis in a Patient With a Family History of Clinically Variable Venous Thromboembolic Events: A Case Report

Antithrombin (AT III) is a potent inactivator of thrombin and factor Xa and plays a major role in the inhibition of coagulation. Inherited deficiencies of AT III are rare and pose a risk of developing venous thromboembolic disease. They can be subdivided into type I (quantitative) or type II (qualitative). Mild AT III deficiency is associated with a 2.4- to 3.5-fold risk of venous thromboembolism (VTE). Thrombosis in patients with AT III deficiency predominantly manifests as a deep vein thrombosis and may subsequently present as pulmonary embolism. It can also occur in uncommon sites such as cerebral, retinal, mesenteric, portal, hepatic, and splenic veins. We report a case of an unprovoked cerebral venous thrombosis in a 24-year-old Omani male, without any comorbidity, who was found to have quantitative deficiency of AT III. He has a significant history of family members having VTE in varying venous beds. This case highlights the wide spectrum of clinical manifestations of quantitative deficiency of AT III and stresses on the importance of taking a good family history and the need for testing for inherited thrombophilia since it can alter long-term management.