An Unexpected Cause of Iliofemoral Venous Thrombosis

A 40-year-old woman with sickle cell trait presents to the emergency department with complaints of left lower limb pain and swelling that started 3 days ago. She is an active smoker for the last 15 years and smokes a pack per day. She occasionally takes omeprazole for gastroesophageal reflux disease symptoms. She has a history of anaphylactic shock that occurred 1 year ago. She denies any recent long-distance travel, surgery requiring immobilization, insect bite or the use of oral contraceptives. She states that her work requires her sitting for approximately 10 hours per day, with only a few breaks. Her vital signs at the emergency department are: 121/60 mmHg, 99.7°F, 96 bpm, 15 respirations per minute and 98% blood O2 saturation. Electrocardiogram and arterial blood gases are normal. Physical examination reveals a tender left thigh/calf, edema, warmth, and redness. Duplex ultrasound detects an extensive deep venous thrombosis from the left common iliac to popliteal vein. Thrombophilia screening detects no abnormalities. The patient is treated with low molecular weight heparin and is discharged on warfarin. After 1 week, she returns to the emergency department because of recurrent pain in her left leg, despite treatment with warfarin. The patient is treated with thrombolysis, and subsequent intravascular ultrasound demonstrates a severe left common iliac vein stenosis from a venous spur. The following day a stent is placed in the stenotic lesion and the patient shows clinical improvement. After 3 days of hospitalization, the patient is discharged home on warfarin for at least 6 months.

Which is the cause of deep venous thrombosis in this patient?

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