Sudden thrombosis of deep veins (DVT) in the legs is a common (1 in 1000/every year) serious disease. Apart from the risk of a deadly pulmonary embolism at the early stage, it might cause deep venous insufficiency leading to venous ulcer after many years.

Immobilization due to surgery (especially orthopedic interventions ) or long flights, hormonal changes, some cancers or congenital defects in blood factors preventing clot formation, might lead to DVT.

It usually causes pain and swelling. Vascular ultrasound is necessary for accurate diagnosis. In cases with suspicion of pulmonary emboli, lung CT and echocardiography are also performed.

Clot preventing drugs (oral factor Xa inhibitors or subcutaneous injection of low molecular heparins) should be started as soon as possible in order to prevent pulmonary emboli and propagation of the clot in the leg veins. In some patients with DVT in larger veins in the abdomen, catheter-based minimal invasive therapies (infusing clot-busting drug through a catheter placed in the vein under local anesthesia or placement of filters) are used. Oral warfarin or factor X inhibitors are used for maintenance therapy after one week. The duration of therapy is dependent on the location, extent and the cause of DVT.

Nearly two out of three patients with DVT develop deep venous insufficiency called post-thrombotic syndrome. During the healing of clot in the deep veins, the venous valves might be damaged, leading to reflux of blood down to the ankle. The pooling of blood might lead to skin ulcers. The risk of post-thrombotic syndrome and the risk of new DVT, are evaluated by duplex scanning and special blood tests during follow up of patients. In patients with severe deep venous reflux, special varicose vein stockings are necessary for the prevention of skin ulcers. In patients with some genetic coagulation disorders ( like homozygous Factor V- Leiden mutation), lifetime clot preventing medications should be used for prevention of new DVT. Maintenance therapy in order to prevent complications should be tailored to each patient. 

In patients with the serious post-thrombotic syndrome, some type of venous surgery (removal of secondary varicosities or ablation of perforators) might be necessary.