Swollen ankles are common during pregnancy or immediately following an injury, but if your ankles are swelling mainly at night, you may have an underlying medical condition. The swollen ankles may be accompanied by other symptoms that make it easier to determine the cause, but see your doctor for diagnosis and treatment.
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Heart Failure and Polyuria
Congestive heart failure can cause swollen ankles. Your weakened heart is unable to pump blood effectively, which causes a buildup of fluid in your limbs. Swelling in the ankles and legs is called peripheral edema; it is typically caused by right-sided heart failure. This may lead to nocturnal polyuria, or frequent urination at night. Your body converts the excess fluid into urine, resulting in you waking up repeatedly during the night to urinate. Other symptoms of heart failure include excessive tiredness and shortness of breath.
An impediment to blood flow from the legs to your heart also can cause nighttime swelling. The swelling may disappear by morning because lying horizontally negates the effect of gravity pulling blood into the legs. Varicose veins are a possible cause. To assist blood moving up the legs, your veins have one-way valves spaced a few inches apart. With varicose veins, the valves leak and the elevated pressure prohibits blood drainage, potentially causing swelling and poor circulation. Another possibility is lymphedema, a condition characterized by blockages in the vessels of the lymph system that cause fluid buildup and swelling.
A gynecological disorder may impede blood flow from the legs to the heart, leading to swollen ankles at night that appear normal by morning. Ovarian cysts or uterine fibroids can restrict blood flow and press on your bladder, leading to increased urination. Ovarian cysts are liquid-filled growths that usually are benign. You might have cysts on your ovaries that do not cause symptoms. Cysts generally disappear on their own but may cause complications such as pain during intercourse, lower abdominal pain and ovarian cancer. Uterine fibroids are growths on the uterus; they are noncancerous and rarely cause symptoms.
An ankle sprain can lead to swelling at night, as can common sprain-type injuries such as ankle bone fractures, tears in the outside ligaments of the ankles and injuries to the ankle tendons or nerves. You also may experience ankle instability, difficult walking, tenderness, pain and stiffness. An ankle sprain may require only basic treatment, such as ice, rest, an elastic ankle support and elevation. Ankle sprain type injuries are usually more serious and may require immobilization, medication to reduce swelling and physical therapy.