From Negative Duplex to Phlegmasia in Minutes: Bedside POCUS Identifies Rapid Thrombosis Unmasking Underlying May-Thurner Syndrome.

May-Thurner syndrome occurs from an anatomical variant in which the left common iliac vein is compressed against the lumbar spine by the overlying right common iliac artery. This often leads to chronic venous stasis predisposing individuals to left-sided iliofemoral deep venous thrombosis (DVT). Progression to phlegmasia cerulea dolens (PCD) is rare, but potentially limb-threatening. Here we describe rapid formation of DVT leading to PCD first discovered during a bedside point-of-care ultrasound (POCUS). A 50-year-old female presented to the emergency department (ED) with left leg swelling following a recent hospitalization for ulcerative colitis flare with rectal bleeding. In hospital she was treated with corticosteroids and had anticoagulation medication held due to active bleeding. On initial presentation to the ED, a comprehensive duplex exam performed by a vascular sonography technician was negative for DVT, as were the physical exam findings. As there was no concern for DVT, a POCUS was performed in an educational context, with the intention of demonstrating consistent imaging findings. However, POCUS performed just 14 min after completion of the duplex exam identified a rapidly evolving thrombus. The patient's leg pain and edema also progressed with discoloration and paresthesia prompting computed tomography angiography (CTA) imaging and vascular consultation for developing phlegmasia. She was taken emergently to the operating room and was subsequently found to have underlying May-Thurner Syndrome (MTS). The patient required a second vascular intervention and was discharged with a complete recovery. This case highlights the critical role of POCUS in detecting evolving vascular emergencies as it changed the patient's treatment plan, expedited diagnosis, and resulted in successful endovascular interventions.