Post-Thrombotic Syndrome

Post-thrombotic syndrome is a long-term leg problem that develops after deep vein thrombosis, a blood clot in a large vein between the leg muscles. Symptoms include heaviness, pain, swelling, and skin changes in the leg that had the clot. According to a 2014 scientific statement from the American Heart Association (AHA), about 20 to 50 percent of people develop this syndrome after deep vein thrombosis, and about 5 to 10 percent develop a severe form. Deep vein thrombosis itself is covered on the Deep Vein Thrombosis page.

How the Syndrome Develops

A clot in a deep vein can damage the one-way valves inside the vein. Damaged valves let blood flow back down. In some people, leftover clot or scar tissue also narrows the vein, so blood flow is obstructed. As a result, pressure in the leg veins stays high, especially when standing and walking. Over time, fluid seeps into the tissues, the skin darkens and hardens, and in severe cases wounds form around the ankle (venous ulcers).

Symptoms That Come and Go

Symptoms usually get worse in the afternoon or after standing and walking for a long time, then ease with rest and the legs raised. Severity varies, from mild heaviness to swelling and wounds that limit activity. The diagnosis can only be made after the early phase of the clot has passed, usually three to six months, because swelling and pain in the first weeks are still part of the clot itself.

Part of Chronic Venous Disease

Post-thrombotic syndrome is a form of chronic venous disease with a secondary cause, namely a clot. Its skin changes and swelling resemble those of venous disease caused by weak valves without a history of clots, covered on the Chronic Venous Insufficiency page. In some people with a clot in the left leg, the blockage comes from a compressed pelvic vein, covered on the May-Thurner Syndrome page.

It Can Be Controlled

This syndrome usually does not go away completely, but its symptoms can be controlled with compression stockings, exercise, skin care, and in selected cases a procedure on the vein. The main preventive step is regular anticoagulant treatment from the time deep vein thrombosis is diagnosed, along with preventing repeat clots in the same leg. Other types of venous disease are covered on the Venous Disease page.

Post-thrombotic syndrome is diagnosed from symptoms and a physical examination in people who have had deep vein thrombosis. The assessment is done after the early phase has passed, usually three to six months after the clot, because swelling and pain in the early period are still part of the clot itself. Doctors use the Villalta scale, which adds up five symptoms, such as pain, cramps, and heaviness, and six signs in the leg, such as swelling, skin hardening, and color changes. A score of 5 or more indicates post-thrombotic syndrome, and the presence of a wound indicates a severe form.

Duplex ultrasound is used to look for leftover clot, narrowing, and leaking valves, and to rule out a new clot if symptoms suddenly get worse. If a long-standing blockage in a pelvic vein is suspected and a stent is being considered, the doctor may order CT or MR venography. Before strong compression stockings are used, blood flow in the leg arteries is assessed if the foot pulses are weak.

Make an appointment with a doctor if the leg that had deep vein thrombosis still feels heavy, painful, or swollen after several months, or if the skin starts to change. Get checked right away if swelling and pain appear suddenly, and go straight to the emergency room if you have sudden shortness of breath.

• A heavy, aching, or swollen leg that interferes with your activities
• Skin around the ankle that darkens, itches, or hardens
• A wound on the leg that does not improve within two weeks
• Bursting leg pain when walking
• Swelling and pain that appear suddenly, a possible sign of a new clot
• Compression stockings that feel too painful or cannot be worn