Deep vein thrombosis is the formation of a blood clot (thrombus) in a deep, interior vein (as opposed to varicose veins). When a vein is inflamed (phlebitis) it often forms a thrombus, which restricts blood flow through the vein. A portion of the clot can break away and travel through the veins to the lungs. Blockage of a large vessel in the lungs, called a pulmonary embolism, may cause serious complications and possibly death.

Causes

Blood clots most commonly occur when the innermost layer of a blood vessel is damaged by infection, surgery, or a previous thrombosis. If damage occurs, blood clots can develop when the same clotting factors that stop external bleeding begin to function inappropriately in deep veins. The clot will form in a vein valve cup, and may grow large enough to block the vein, or become dislodged and travel to the lungs.

If the blockage is not treated, it can jeopardize an affected limb by obstructing blood flow. This causes leg swelling and can lead to chronic venous insufficiency (CVI).
Less common causes of thrombosis are:
Lengthy periods of immobility (such as sitting on an airplane or confinement to bed or wheelchair). These can disrupt the balance of blood pressure in the veins, slow circulation and impair blood flow.
Clotting abnormalities associated with cancer, sickle-cell anemia, estrogen or progestin replacement therapy, dehydration and thickening of the blood.

Warning Signs

• Approximately half of those with deep vein thrombosis never have recognized symptoms. The symptoms are:
• Sudden, continuous deep pain in the calf or thigh
• Deep pain in a leg which increases, either when exercising or from standing for long periods
• Frequent redness and swelling
• Warm skin
• Leg fatigue
• Surface veins become more visible

Treatment & Prevention

Thrombosis in varicose or superficial veins is normally treated with anti-inflammatory drugs, together with elevating the legs to reduce pressure.
Deep vein thrombosis is immediately treated with anticoagulants (blood thinners), together with bed rest and elevation of the legs above heart level to reduce pressure and promote the flow of blood back to the heart. If blood thinners are used for long-term treatment, patients are cautioned not to take certain other medications, especially aspirin, which may interact with them.

When a patient resumes walking, elastic compression of the lower leg controls swelling, collapses the superficial veins and increases blood flow in the deep veins to promote healing. If there is an associated venous ulcer of the ankle, this same treatment promotes healing.

People who are vulnerable to blood clots should not smoke, because tobacco promotes clot formation.

Resources

Vascular Disease Foundation

National Heart, Lung and Blood institute

WebMD