Swelling in only one foot, known as unilateral foot swelling, often indicates a localized problem, unlike general swelling affecting both feet. While some causes are minor, others signal serious underlying conditions requiring prompt medical attention. Understanding these potential reasons is important for seeking appropriate care.
Sudden and Urgent Causes
Unilateral foot swelling can arise rapidly from conditions that demand immediate medical evaluation. Injuries are a common culprit, as direct trauma to the foot or ankle can lead to swelling. An ankle sprain occurs when ligaments are stretched or torn, causing pain, bruising, and swelling as fluid accumulates. Fractures of bones in the foot or ankle can also result in significant swelling due to internal bleeding and the body’s inflammatory response.
Infections also present as sudden and urgent causes of unilateral foot swelling. Cellulitis, a bacterial infection of the skin and underlying tissues, typically manifests with rapidly spreading redness, warmth, pain, and swelling in the affected area. This infection can occur anywhere but frequently affects the lower legs and feet, sometimes accompanied by fever and a general feeling of being unwell. Abscesses, localized collections of pus under the skin, can also cause acute swelling, warmth, and pain.
A particularly serious cause of sudden, unilateral leg or foot swelling is deep vein thrombosis (DVT), which involves a blood clot forming in a deep vein, most commonly in the leg. DVT can cause sudden onset of swelling, often accompanied by pain, tenderness, warmth, and a reddish or discolored appearance in the affected leg or calf. This condition is concerning because a portion of the clot can break off and travel to the lungs, leading to a life-threatening pulmonary embolism, characterized by sudden shortness of breath and chest pain.
Gradual or Persistent Conditions
Some conditions causing unilateral foot swelling develop more gradually or represent chronic issues. Lymphedema is characterized by impaired drainage of lymph fluid, leading to its accumulation in tissues. It can result from genetic factors (primary lymphedema) or be secondary to surgery, radiation, infection, or trauma that damages the lymphatic system. The swelling in lymphedema can make the foot feel heavy or tight, and while sometimes pitting (leaving an indentation when pressed), it can also be non-pitting, often affecting the toes.
Chronic venous insufficiency (CVI) occurs when leg vein valves do not function properly, hindering blood return to the heart and causing blood to pool in the lower limbs. While CVI can affect both legs, it may present unilaterally if veins in one leg are more significantly impacted. Symptoms often include swelling that worsens with prolonged standing and improves with elevation, along with skin changes such as discoloration, thickening, and sometimes the development of ulcers.
Inflammatory types of arthritis can also cause localized swelling in one foot or ankle joint. Gout, for example, is a form of inflammatory arthritis caused by uric acid crystal buildup in a joint, typically affecting the big toe but also capable of affecting the ankle or other foot joints. A gout attack causes sudden, intense pain, redness, warmth, and swelling in the affected joint. Other forms of arthritis, such as psoriatic arthritis or localized osteoarthritis, can also lead to inflammation and swelling in a single joint of the foot or ankle.
Less common, but possible, causes of unilateral foot swelling include cysts or tumors. A ganglion cyst, a fluid-filled sac near joints or tendons, can cause a lump and localized swelling, particularly if it presses on nerves or surrounding tissues. While often benign, they may cause discomfort. Rarely, benign or malignant tumors in the foot or ankle area can cause swelling by obstructing fluid flow or by direct tissue expansion and inflammation.
Knowing When to Get Help
Recognizing when unilateral foot swelling warrants medical attention is important for proper diagnosis and timely intervention. Certain “red flags” indicate a need for immediate evaluation. These include sudden, severe pain with swelling, significant redness or warmth, or fever and chills.
If swelling rapidly worsens, or if there is calf tenderness, inability to bear weight, or associated symptoms like shortness of breath or chest pain, seek immediate medical care. These could indicate serious conditions requiring urgent treatment.
It is advisable to consult a healthcare professional if unilateral foot swelling is persistent, unexplained, or accompanied by any other concerning symptoms. A medical provider will conduct a physical examination and may recommend diagnostic tests like ultrasound, blood tests, or X-rays to pinpoint the underlying cause. Self-diagnosis is not recommended; professional medical advice is crucial for determining the correct diagnosis and establishing an effective treatment plan.