When a clot develops in a deep vein of the limb (leg or arm or pelvis) we call it a Deep Vein Thrombosis (DVT). This causes the leg to swell and become painful. It is important to have this correctly diagnosed since treatment to stop the clot enlarging and moving through the circulation to the heart and lungs (pulmonary embolus) is usually needed. This involves thinning the blood with heparin injections and then an oral anticoagulant (warfarin, rivaroxaban, etc..). The deep veins of the leg may be damaged by the thrombosis and fail to work normally after a DVT. The swelling and pain in the leg long term after a DVT is sometimes called Post Thrombotic Syndrome (PTS)
What Causes a DVT ?
There are many factors that can cause a DVT to occcur. In the deep veins of the leg, if the blood flow is slow, or the vein wall is damaged / diseased or the blood itself is more prone to clot (thicker blood) then a clot forming in the vein becomes more likely. This triad of factors (VEIN, BLOOD, FLOW) is the model used to explain why a clot may have occurred. Often referred to as Virchows Triad.
Slower blood flow occurs when people are immobile due to illness or injury, when travelling in restriced positions for many hours, after surgery, with dehydration, increasing age and obesity. The vein wall may be more prone to a clot after injury, limb surgery, previous DVT, infusion with drugs and fluids that damage the vein lining. The blood can be more likely to clot due to medications, (hormones, the pill) in patients with cancer and in conditions where the blood count is raised (polycythaemia, leukaemia). Some patients have inherited conditions with abnormal clotting factors and are more prone to DVT as a result.
With thinning of the blood, the clotting process can usually be controlled. Over 3-6 months the clot in the vein is slowly resorbed and often the vein "recanalises" so that blood can flow through it again. 10-20% of veins may remain blocked. The valves in the veins are often damaged in this process, and the deep veins often do not work as efficiently as normal after a DVT.
There is growing interest in using clot dissolving drugs, and devices within the clotted veins to remove the clot when it first forms. This is called mechanico-lysis. For large extensive clots in the leg and pelvis, there is some evidence that this early removal of the clot can improve the function in the leg veins rather than leaving the clot to slowly be resorbed or leave the vein blocked. On going studies are evaluating this treamtent, to see which patients benefit most from this treatment.
If the venous system in the leg fails to work normally the pressure in the leg veins rises. This damages the circulation in the lower leg particularly around the ankle leading to swelling, discomfort, skin changes and eventually it can cause ulceration. Varicose veins, a DVT, or primary failure of the valves in the veins can all contribute to this. There are some simple measures to help the circulation in the leg veins, (elastic stockings, walking, avoiding standing, elevation, weight control) which are all very important in the management of this problem. Occasionally procedures on the veins may help, particularly if the problem is mainly in the superficial veins.
Post Thrombotic Syndrome PTS
PTS refers to the occurrenc of venous insufficiency with the above symptoms of pain, swelling, skin changes etc... in a leg after DVT. This often occurs in the first 1-2 years after the DVT. Some evidence of symptoms and signs is present in 50% of cases after DVT, but it is only severe in 10-20% of cases. Good anticoagulation after the DVT, keeping mobile, avoiding being overweight, can all help reduce PTS. There is some debate about the effectivenes of wearing support stckings and for how long in order to reduce PTS. They probably help to some extent, especially early on after the DVT when the leg is swollen to improve symptoms. Some suggest wearing them for 2 years, but this may not always be necessary.
For more information go to Circulation Foundation