Postthrombotic syndrome (also called postphlebitic syndrome) is a complication of a blood clot that forms in a deep vein. Postthrombotic syndrome occurs because of damage to the vein caused by the blood clot (thrombosis).

Veins have valves that prevent blood from flowing the wrong way. These valves keep blood flowing toward the heart. Blood clots can damage the veins and valves, preventing blood from flowing back to the heart properly. As a result, blood collects in the area normally drained by the vein. The pressure from the buildup of blood causes small blood vessels (capillaries) to burst and bleed slightly.

The symptoms of postthrombotic syndrome include:

• Brownish discoloration of the skin.
• Itching, swelling, slow-healing sores, and pain in the area.
• Fragile skin on the area that bruises easily. The skin may be dry and may peel.

Postthrombotic syndrome can increase the risk for forming additional blood clots in the affected area. It can also occur in other areas with deep vein clots, such as in an arm.

Medicines called thrombolytics may be used to dissolve large blood clots and prevent postthrombotic syndrome. Specially fitted compression stockings may be used for prevention and treatment of postthrombotic syndrome.