Introduction: Antiphospholipid syndrome (APS) is a rare autoimmune disorder characterized by increased propensity to thrombotic events, pregnancy complications and persistent presence of antiphospholipid antibodies (1). Although relatively uncommon, APS has significant clinical importance due to potentially life-threatening complications. In APS patients, thrombotic events represent the most common syndrome manifestation. Deep vein thrombosis with pulmonary embolism is the most common manifestation (2). APS can be primary (isolated) or secondary, associated with other autoimmune diseases, most commonly systemic lupus erythematosus (SLE), where 30-40% of SLE patients have antiphospholipid antibodies (3).

Case report: 22-year-old male patient, who presented to the Emergency Department with dyspnea during physical activity, followed by collapse and loss of consciousness. MSCT pulmonary angiography confirmed thromboembolic disease of large pulmonary artery branches bilaterally, with pericardial effusion. Treatment was immediately initiated with therapeutic-dose low-molecular-weight heparin. From the sixth day of hospitalization, peroral anticoagulant therapy with warfarin was introduced. Laboratory findings showed a positive ANA titer 1:320 with cytoplasmic and punctate pattern, elevated anti-dsDNA (31 H), and positive beta-2 glycoprotein I antibodies (37.9). Lupus anticoagulant was negative. These findings combined with clinical presentation confirmed antiphospholipid syndrome diagnosis. Multidisciplinary treatment approach included rheumatological follow-up with introduced hydroxychloroquine 200 mg daily, along with regular hematologist and cardiologist controls. Continuation of anticoagulant therapy and serological marker monitoring is recommended. Follow-up immunological workup is planned three months after initial testing to confirm antiphospholipid antibody persistence.

Conclusion: This case illustrates APS as a significant diagnosis in young adults with unexplained pulmonary embolism. Early diagnosis and timely anticoagulant treatment are crucial for preventing recurrent thrombotic events. A multidisciplinary approach with regular monitoring enables optimal management of this complex autoimmune disorder.