(See also Overview of the Venous System.)
Superficial venous thrombosis most often affects the superficial veins (located just under the skin) in the legs but may also affect superficial veins in the groin or in the arms. Superficial venous thrombosis in the arms usually results from having an IV. Superficial venous thrombosis in the legs usually results from varicose veins. However, most people with varicose veins do not develop blood clots (thrombosis).
Even a slight injury can cause a varicose vein to become inflamed (phlebitis). Unlike deep vein thrombosis, which causes very little inflammation, superficial venous thrombosis involves a sudden (acute) inflammatory reaction that causes the blood cot (thrombus) to adhere firmly to the vein wall and lessens the likelihood that it will break loose. Unlike deep veins, superficial veins have no surrounding muscles to squeeze and dislodge a blood clot. For these reasons, superficial venous thrombosis rarely causes a blood clot to break loose (embolism).
Migratory phlebitis or migratory thrombophlebitis is superficial venous thrombosis that repeatedly occurs in normal veins. It may indicate a serious underlying disorder, such as cancer of an internal organ. When migratory phlebitis and cancer of an internal organ occur together, the disorder is called Trousseau syndrome.
Pain and swelling develop rapidly in the area of inflammation. The skin over the vein becomes red, and the area feels warm and is very tender. Because blood in the vein is clotted, the vein feels like a hard cord under the skin, not soft like a normal or varicose vein. The vein may feel hard along its entire length.
Doctors recognize superficial venous thrombosis by its appearance. Tests are not usually needed, although if people have superficial venous thrombosis above the knee that developed suddenly and not in an area of varicose veins, doctors often do ultrasonography to see if there is a blood clot in the deep veins.
Most often, superficial venous thrombosis subsides by itself. Applying warm compresses and taking an analgesic, such as aspirin or another nonsteroidal anti-inflammatory drug (NSAID), usually help relieve the pain.
Although the inflammation generally subsides in a matter of days, several weeks may pass before the lumps and tenderness subside completely. Sometimes people who have very extensive superficial venous thrombosis are also given heparin or a different anticoagulant to help limit the blood's clotting.