<![CDATA[Paget-Schroetter Syndrome (PSS), also known as effort thrombosis, is a rare form of primary upper extremity deep vein thrombosis (UEDVT) caused by compression of the subclavian–axillary vein at the thoracic outlet. It typically affects young, healthy individuals following strenuous physical activity. Due to its potential for long-term morbidity, proper diagnosis and appropriate anticoagulation management are essential. Case Presentation: A 24-year-old healthy male presented with a three-day history of sudden swelling, erythema, pain, and numbness in his left upper extremity. Symptoms emerged several hours after playing basketball. Physical examination revealed significant edema of the left arm, although peripheral pulses remained intact. Laboratory investigations showed a markedly elevated D-dimer level of 4249.03 ng/mL, while coagulation profiles were within normal limits. Doppler ultrasound confirmed thrombosis in the left subclavian and axillary veins. The patient was diagnosed with PSS and initiated on oral rivaroxaban (15 mg once daily). At the two-week follow-up, the D-dimer level had decreased to 1789 ng/dL with clinical improvement. After one month of therapy, the edema had completely resolved, and the D-dimer level normalized to 372 ng/mL. Consequently, anticoagulation therapy was discontinued, and the patient was scheduled for long-term monitoring. Conclusion: This case highlights the classic presentation of Paget-Schroetter Syndrome in a young athlete. Early recognition and the use of direct oral anticoagulants (DOACs) such as rivaroxaban can lead to rapid clinical resolution and normalization of laboratory markers. A high index of suspicion is required when evaluating acute unilateral arm swelling in young individuals following physical exertion]]>
