There are more causes of swelling in the left foot, which may be caused by arthritis or poor vascular return in the lower extremities, and needs to be differentiated from edema caused by nephritis and edema caused by poor cardiac function. Swelling due to organ function problems are bilaterally symmetrical, and unilateral limb swelling is often a local problem, such as foot edema due to arthritis, and lower limb edema due to rheumatoid arthritis and ankylosing spondylitis. Unilateral edema is more likely in ankylosing spondylitis, and unilateral joint edema can also occur in reactive arthritis. Unilateral limb edema can occur in middle-aged and older adults with poor venous return, such as thrombosis in the veins that blocks venous return. Patients who present with this manifestation should actively seek medical attention to determine the diagnosis and develop a treatment plan based on clinical examination.