Many of the factors that need to be considered in elderly people with edema of a single foot and neck are local factors, such as trauma. Edema caused by trauma has a clear history and the patient can have a clear memory of it. If the edema is caused by mosquito bites or inflammation, with painful sensation or redness, it is easier to differentially diagnose. If the above conditions are ruled out, the most to be considered is the unilateral appearance of thrombus in the elderly, the formation of thrombus is badly related to the return of blood to the lower limbs of the elderly, or the elderly have other underlying diseases causing the formation of thrombus. If you want to rule out the possibility of thrombosis, you need to do vascular ultrasound of the lower extremities, including arteries and veins, to clarify the presence of thrombosis. If thrombosis does exist, the cause should be actively searched and treated in order to better recover the edema of the foot and neck.