Paediatric Antiphospholipid Syndrome Presenting With Intracardiac Thrombosis and Extensive Pulmonary Embolism: A Case Report

Background Antiphospholipid syndrome (APS) is an autoimmune disorder characterised by arterial, venous, or microvascular thrombosis. Intracardiac thrombosis (ICT) is a rare but life‐threatening manifestation, particularly in the paediatric population, and its coexistence with extensive pulmonary embolism (PE) is underreported. Case Presentation A 13‐year‐old male with ulcerative colitis presented with progressive dyspnoea, chest pain, and tachycardia. CT pulmonary angiography revealed extensive bilateral PE with right ventricular strain. Echocardiography showed severe right ventricular enlargement, systolic dysfunction, and two right ventricular apical thrombi. Lupus anticoagulant was positive on two occasions 12 weeks apart, confirming APS. The patient was initially anticoagulated with rivaroxaban but developed recurrent iliofemoral deep vein thrombosis within 30 days. After switching to warfarin, no further thrombotic events occurred, and follow‐up imaging demonstrated thrombus regression. Conclusion Paediatric APS can present with life‐threatening ICT and extensive PE. Early recognition, appropriate anticoagulation with vitamin K antagonists, and awareness of the limitations of direct oral anticoagulants are essential to prevent recurrence and improve outcomes.