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Causes of Leg Swelling (Edema)
Leg swelling results from accumulation of fluid in the interstitial tissues. Causes are broadly divided by whether the swelling is bilateral or unilateral, which helps narrow the diagnosis (Harrison's, p. 7797).
Bilateral Leg Swelling
These causes reflect systemic pathology:
| Category | Cause | Mechanism |
|---|---|---|
| Cardiac | Congestive heart failure (CHF) | Raised venous hydrostatic pressure → fluid leaks into tissues |
| Renal | Nephrotic syndrome | Hypoalbuminemia → reduced oncotic pressure |
| Hepatic | Cirrhosis / severe liver disease | Hypoalbuminemia + portal hypertension |
| Endocrine | Hypothyroidism (myxedema) | Glycosaminoglycan deposition; non-pitting edema |
| Endocrine | Graves' disease (pretibial myxedema) | Autoimmune tissue deposition |
| Nutritional | Protein malnutrition (kwashiorkor) | Low serum albumin → reduced oncotic pressure |
| Medications | Dihydropyridine calcium channel blockers (e.g., amlodipine), thiazolidinediones, steroids, NSAIDs | Arteriolar dilation or sodium/water retention |
| Venous | Chronic venous insufficiency | Incompetent valves → venous hypertension |
| Lymphatic | Primary/secondary lymphedema | Impaired lymph drainage |
| Idiopathic | Idiopathic edema (mostly women) | Unknown; possibly capillary leak |
Unilateral Leg Swelling
These causes are typically localized:
| Cause | Key Feature |
|---|---|
| Deep vein thrombosis (DVT) | Acute onset, calf tenderness, risk factors (immobility, malignancy, surgery) |
| Cellulitis | Erythema, warmth, tenderness; may have fever |
| Chronic venous insufficiency | Gradual, varicosities, skin changes (lipodermatosclerosis) |
| Lymphedema | Non-pitting, "brawny" edema; often dorsum of foot involved |
| Ruptured Baker's (popliteal) cyst | Posterior knee pain preceding swelling |
| Muscle tear / hematoma | History of trauma or exertion |
| Peripheral artery disease / ischemia | Associated with pain, pallor, absent pulses |
Pathophysiological Mechanisms
Edema occurs when one or more of the following are disrupted:
- Increased capillary hydrostatic pressure (e.g., CHF, venous obstruction)
- Decreased plasma oncotic pressure (e.g., hypoalbuminemia from liver/kidney disease)
- Increased capillary permeability (e.g., infection, inflammation, allergic reaction)
- Lymphatic obstruction (e.g., post-surgical, filariasis, malignancy)
- Sodium and water retention (e.g., renal failure, drug-induced)
Clinical Clues
- Pitting edema → fluid accumulation (cardiac, renal, hepatic)
- Non-pitting edema → lymphedema or myxedema
- Bilateral + ascites + jaundice → hepatic cirrhosis
- Bilateral + dyspnea + raised JVP → heart failure
- Unilateral + acute + warm → DVT or cellulitis
Always evaluate with history, physical exam, and targeted investigations (BNP, albumin, renal function, Doppler ultrasound for DVT, TSH) to identify the underlying cause.
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