Edema of the lower extremities in pleural effusion may be caused by hypoproteinemia, renal failure, heart failure, and lower extremity venous thrombosis. 1. Hypoproteinemia: In severe hypoproteinemia, pleural effusion and edema of the lower extremities occur due to abnormal osmotic pressure. It may be due to malnutrition or to liver diseases such as cirrhosis. 2. Renal failure: In renal failure, edema of the lower extremities may occur due to impaired renal excretory function and sodium retention. When sodium retention is severe, the circulatory system will be affected and pleural effusion will occur. 3. Heart failure: in heart failure, the heart muscle is damaged, contraction weakness, poor blood circulation, sodium retention, pulmonary circulation stasis, pleural effusion, physical circulation stasis, lower extremity edema. 4. Lower extremity venous thrombosis: lower extremity venous thrombosis, especially deep vein thrombosis, the affected limb blood circulation is blocked, lower extremity edema, thrombus dislodgement, embolism in the lungs occurring pulmonary embolism, pulmonary arterial circulation is blocked, pleural effusion occurs, then it will show pleural effusion lower extremity edema. Pleural effusion lower extremity edema, need to go to the hospital to do a systematic examination, clear condition after active diagnosis and treatment.