Deep Vein Thrombosis is the development of a blood clot (thrombus) in the deep veins of the legs, pelvis, or arms. Clots can form in superficial veins (called superficial thrombophlebitis or simply "phlebitis") and in deep veins. While blood clots in superficial veins rarely cause serious problems, clots in deep veins require immediate medical evaluation. Deep veins that lie near the center of the leg are surrounded by powerful muscles that contract and force deoxygenated blood back to the lungs and heart. One-way valves prevent the back-flow of blood between the contractions. (Blood is squeezed up the leg against gravity and the valves prevent it from flowing back to our feet.) When the circulation of the blood slows down due to illness, injury or inactivity, blood can accumulate or "pool" which provides an ideal setting for clot formation. Blood clots in deep veins can grow in size, break loose, and then travel through the bloodstream to the lungs, resulting in life-threatening pulmonary embolism (See below). Deep vein thrombosis can cause other long-term complications. In about 25% of cases, deep vein thrombosis damages the affected vein and leads to long-lasting post thrombotic syndrome. This condition can cause pain, swelling, discoloration, and leg sores.
Blood clots can form in veins when you are inactive for example, if you are paralyzed or bedridden or must sit while on a long flight or car trip. Deep vein thrombosis has also been referred to as "Economy Class Syndrome" due to the occurrence after sitting on long flights.
Symptoms of deep vein thrombosis include generalized swelling of the affected leg. When measured, the affected leg may be larger than the other leg. Also, your affected leg may feel warm and be redder than the other leg. You may have pain or tenderness in the calf or thigh when it is touched or squeezed or with movement or standing. Calf or thigh pain may become constant and increase with squeezing or movement.