What is post thrombotic syndrome? Why is it so debilitating and can it be treated?

Deep vein thrombosis (DVT) is a potentially fatal blood clot that occurs in the deep veins of the leg or arm. If left untreated, a DVT can result in a pulmonary embolism (PE) which is a blood clot that breaks off from the leg or arm and travels to the lung. A PE can be fatal with nearly 25% of patients presenting with sudden death as their 1st symptom!

Regardless of the size or location of the clot, blood thinning medication (also known as anticoagulation) is the standard of care for the treatment of DVT. Many patients and health care providers do not realize that blood thinners do NOT dissolve the clot. Rather they keep the blood “thinned” so that the clot does not get worse. It is the body’s own clot-busting mechanism that breaks down the clot. Unfortunately with extensive clot that spans the entire leg, the body just cannot break down the clot effectively and instead leaves behind scar tissue.


FIG 1: Acute DVT is less than 14 days old and looks like grape jelly.

FIG 2: Inside of a healthy vein

Acute DVT is less than two weeks old, looks like grape jelly (FIG 1), and can often be easily removed or sucked out of the veins using minimally invasive techniques (known as thrombolysis or thrombectomy) pioneered by interventional radiologists. In experienced hands, these techniques are safe and carry a low risk of complications, resulting in quick resolution (often within 24-48 hours) of pain and swelling. Subacute DVT is over 14 days old and chronic DVT is 30 days old or greater. Thrombolysis is ideally meant for acute and subacute DVT and is ineffective for chronic DVT (FIG 2).

Patients with extensive DVT that goes from the groin/pelvis all the way down to the ankle (known as iliofemoral DVT) are at the highest risk of developing permanent long-term complications. Symptoms of chronic leg swelling, pain, fatigue, skin discoloration and ulcers can start to occur in 1-2 years after an iliofemoral DVT. Such symptoms are referred to as post thrombotic syndrome (PTS) or post phlebitic syndrome. PTS has its highest incidence of 50% in those patients with iliofemoral DVT. Patients with DVT limited to the femoral and popliteal veins (thigh veins) can also get PTS and patients with calf DVT are much less likely to develop PTS. PTS can also occur in patients with extensive arm DVT.

So can procedures such as thrombolysis prevent PTS? The answer is probably not. This was shown by a multi-center, prospective randomized trial funded by the NIH known as the ATTRACT trial (N Engl J Med 2017; 377:2240-2252). The emphasis on the trial results has been on the fact that thrombolysis does NOT prevent PTS in comparison to anticoagulation alone. However, what is noteworthy and often not discussed is the fact that those patients who underwent thrombolysis had significantly less PTS than those that had anticoagulation alone. 

FIG 3: Scar tissue (synechiae) inside the vein.

Chronic DVT, on the other hand, cannot be removed. The jelly-like clot has now been converted to scar tissue or synechiae (FIG 3) which sticks like glue to the walls of the vein (as shown on the right), thereby restricting blood flow. In addition to slowing down blood flow, the scar tissue acts like “thick glue bands” bringing the walls of the vein together and thereby making the diameter of the vein smaller. For example, the femoral vein in the leg normally has a diameter approximately that of a quarter. If the femoral vein is filled with clot and treated with blood thinners and the body’s own clot busting mechanism, within one year the femoral vein will be open but would have constricted to the diameter of a dime or less. Since the volume of blood within the body is the same, the blood in the lower body is draining through a vein that is half its original size. This leads to the symptoms of PTS.

As blood tries to makes its way back to the heart thru the scar tissue, the body experiences a variety of symptoms. Pain is one of the most common symptoms of PTS. Swelling, fatigue, heaviness, numbness, and tingling are a few others. If the body has developed sufficient venous collaterals (bypass vessels to reroute the blood), the swelling may be minimal. This is often confusing to health care providers who often see these patients and may believe them to be drug seeking as there is no outward sign of chronic DVT to explain their pain. Other less commonly known PTS symptoms include shortness of breath, pelvic pain, pain during intercourse, and heavy bleeding during menstruation.

Can the symptoms of PTS be improved? Yes. In many but not all cases, PTS can be significantly improved. However, the leg will never be completely normal as before the DVT. In centers that specialize in treating chronic dvt, a procedure known as deep venous recanalization can be performed in which small wires (approximately 2 mm in diameter) are introduced into the damaged veins and the “thick glue bands” are broken with a balloon. This allows the vein walls to open up to their normal diameter, thereby allowing blood to drain through them. Depending on the location of the damaged veins, stents can be placed to keep the damaged veins open so that the scar tissue that could not be broken does not constrict the vein walls together and prevent blood from draining.

In 2015, a 44-year-old male with chronic iliofemoral DVT for 5 years and who was nearly wheelchair bound from his PTS symptoms was found to have extensive scar tissue in both legs. He had been told that nothing could be done. After deep venous recanalization, the swelling in his legs dramatically reduced and he remains with minimal symptoms to this day.

PTS is a debilitating complication of DVT that few health care providers truly understand. Unlike peripheral arterial disease (PAD) that mainly affects the elderly, PTS affects patients of all ages who are often in the prime of their lives and have disabling pain and swelling. While there is no cure for PTS, it can be significantly improved. As long as a patient can tolerate blood thinning medication, he/she is likely a candidate for deep venous recanalization.

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