Leg Swelling

Leg swelling reflects fluid accumulating in the tissues, and the single most useful diagnostic question is whether one leg or both are affected. One-sided swelling suggests a local cause: deep vein thrombosis, cellulitis, an injury or lymphatic obstruction. Sudden one-sided swelling with pain, warmth or redness is a medical urgency because DVT can embolise to the lungs. Two-sided swelling suggests a systemic cause: chronic venous insufficiency is the most common, where failing vein valves allow blood to pool during standing, producing swelling that worsens through the day, improves overnight, and eventually causes the brown skin staining and hardening of the lower shin that precede venous ulceration. Heart failure produces bilateral swelling alongside breathlessness. Kidney disease with protein loss, liver disease with low albumin, and hypothyroidism all cause fluid retention. Medications are a major and frequently missed cause, particularly calcium channel blockers such as amlodipine, which produce ankle swelling in a substantial minority of users. Simple dependent oedema from prolonged sitting or standing, heat and pregnancy is common and benign. Compression therapy is the mainstay for venous causes and is consistently under-used.

• •Swelling of one leg, or both, with pitting when pressed
• •Swelling worse at the end of the day and better after a night in bed
• •Tight, heavy or aching legs
• •Shoes and socks leaving deep marks
• •Skin changes: brown staining, thickening or hardening of the lower shin
• •Varicose veins
• •Itching and dry, flaky skin over the shins
• •Sudden one-sided swelling with pain, warmth or redness — possible DVT
• •Breathlessness alongside bilateral swelling — possible heart failure
• •Skin breakdown or ulceration above the ankle

• •Chronic venous insufficiency — the most common cause of bilateral swelling
• •Prolonged standing or sitting, long flights and hot weather
• •Deep vein thrombosis — typically one leg, and urgent
• •Cellulitis, causing one hot red swollen leg
• •Heart failure
• •Kidney disease with protein loss
• •Liver disease with low albumin
• •Medications: calcium channel blockers such as amlodipine, NSAIDs, steroids, pioglitazone, some antidepressants
• •Pregnancy
• •Obesity
• •Lymphoedema, including after cancer surgery or radiotherapy
• •Hypothyroidism
• •Pelvic mass obstructing venous return

Fluid movement across capillaries is governed by hydrostatic pressure pushing fluid out and oncotic pressure from plasma proteins pulling it back. Venous insufficiency and heart failure raise hydrostatic pressure; low albumin from liver or kidney disease lowers oncotic pressure; inflammation and infection increase capillary leak; and lymphatic obstruction prevents drainage of interstitial fluid. Gravity concentrates all of these effects in the legs, which is why elevation and compression — which counteract hydrostatic pressure directly — are effective across most causes.