The cause of edema in the ankle needs to be analyzed according to different situations. If edema appears on one side of the ankle, it may be caused by unilateral localized lesions, such as trauma, inflammation, mosquito bites, unilateral limb, thrombosis and gout nodules, and the differential diagnosis will be made based on the presentation and medical history. If the edema is bilateral, especially in the evening and relieved after rest, it may be caused by poor blood flow to the lower extremities, which is more common in the elderly and requires a urinary ultrasound to confirm. If the edema in the ankles is severe in the morning and is accompanied by puffiness of the eyelids and increased foam in the urine, it may be due to kidney disease, and a series of tests are needed for differential diagnosis. If the edema is accompanied by symptoms of arrhythmia or heart failure, such as inability to lie down at night or palpitations after activity, it is likely that the edema is caused by poor heart function.