Venous insufficiency, a blood clot, lymphedema, and heart, kidney or liver disease can all cause swollen ankles, according to WebMD. Side effects from certain medications, infections, foot and ankle injuries, and complications from pregnancy often cause ankles to swell.
When the veins in the legs and feet weaken and allow blood to leak back down instead of flowing up to the heart, the fluids pool in the soft tissue and cause swelling in the ankles, explains WebMD. In severe cases, ulcers and infection can occur. If a superficial or deep vein blood clot forms in the leg vein and prevents the return of blood to the heart, the ankles and feet may swell. If a clot dislodges and travels to the lungs or heart, a life-threatening emergency exists. Lymphedema occurs when lymphatic fluids build up in the tissue of the feet and legs due to problems with the lymph vessels, preventing wounds from healing and causing infections.
Drugs that can cause ankle swelling include blood pressure medications, estrogen, nonsteroidal anti-inflammatories, steroids and antidepressants, reports WebMD. Some diabetes medications also cause swelling, and individuals with diabetes are at increased risk of swelling from foot infections associated with diabetic neuropathy. While swelling of the ankles and feet is common during pregnancy, pre-eclampsia is a serious condition that manifests as sudden or excessive swelling after the 20th week of pregnancy.