1.Swelling of the affected limb is the most common symptom after lower limb vein thrombosis, and the affected limb has high tissue tension and non-depressed edema. The skin color is reddish and the skin temperature is higher than that of the healthy side. In case of severe swelling, blisters may appear on the skin. The site of swelling varies with the site of thrombosis. In patients with iliac-femoral vein thrombosis, swelling of the entire affected limb is obvious, while in patients with calf plexus thrombosis, swelling is limited to the calf; in patients with inferior vena cava thrombosis, swelling occurs in both lower limbs. If the thrombosis starts in the iliac-femoral vein, the swelling of the thighs appears early. If the thrombus starts in the calf plexus and gradually extends to the iliac-femoral vein, the swelling of the calf appears first and then the thigh is involved. The swelling is most severe on the second or third day after the onset of the disease and then gradually decreases. The decrease in swelling is characterized by a decrease in tissue tone and then by a gradual decrease in the circumference of the affected limb, but it is difficult to change to normal unless the thrombus is completely removed early. In the late stage of thrombosis, although some of the veins have been recanalized, the venous pressure of the affected limb is still high because the venous valve function has been destroyed, and its performance is similar to that of primary lower limb valve insufficiency. 2.The causes of pain and pressure pain are mainly 2: ① Inflammatory reaction caused by thrombus in the vein, which causes continuous pain in the affected limb. ②The thrombus blocks the vein and obstructs the venous return of the lower limb, resulting in distension and pain of the affected limb, which is aggravated when standing upright. The pressure pain is mainly confined to the area where the venous thrombus produces an inflammatory response, such as the femoral vein pathway or the calf. Calf gastrocnemius pressure pain is also known as positive Homans sign. Since squeezing the calf has the risk of dislodging the thrombus, it is not advisable to exert too much force during the examination. 3.Superficial varicose veins belong to compensatory reaction, when the main vein is blocked, the venous blood of lower limb returns through superficial vein, and the superficial vein is compensated to expand. Therefore, superficial varicose veins are usually not obvious in the acute stage, which is a manifestation of the sequelae of venous thrombosis in the lower limbs. 4, femoral cyanosis when DVT of lower limb widely involves intra-muscular venous plexus, because the iliofemoral vein and its lateral branches are all blocked by thrombus, the tissue tension is extremely increased, resulting in arterial spasm of lower limb, limb ischemia or even necrosis. Clinically, the pain is severe, the skin of the affected limb is shiny, accompanied by blisters or blood blisters, and the skin color is blue-purple, which is called painful femoral cyanosis. It is often accompanied by arterial spasm, weakened or absent arterial pulsations in the lower extremities, decreased skin temperature, and consequently a high degree of circulatory disturbance. The patient has a strong systemic reaction with high fever and atrophy, and is prone to shock manifestations and wet gangrene of the lower extremities. 5.Femoral leukodystrophy When acute embolism of the deep veins of the lower extremities, the edema of the lower extremities reaches its highest level within a few hours, the swelling is concave and hypertonic, and the obstruction occurs mainly in the femoral venous system. When combined with infection, the stimulation of the artery continues to spasm, and swelling, skin pallor, and small subcutaneous reticular venous dilatation of the entire extremity are seen, called painful femoral bruising. Femoral cyanosis and femoral leukomalacia are less common and are an emergency condition requiring urgent surgical removal of the embolus to save the affected limb.