What causes leg edema?

Causes of Leg Edema

Leg edema results from an imbalance between capillary filtration and lymphatic drainage, with causes broadly categorized into systemic disorders (bilateral edema) and localized pathology (typically unilateral edema). 1

Systemic Causes (Bilateral Edema)

Cardiac Causes

• Heart failure is a leading systemic cause, resulting from increased central venous hypertension, increased capillary permeability, and plasma volume expansion, producing bilateral pitting edema 1, 2
• Both biventricular failure and heart failure with preserved ejection fraction can lead to pitting edema 2
• Associated symptoms include dyspnea, orthopnea, paroxysmal nocturnal dyspnea, jugular venous distention, S3 gallop, and pulmonary rales 1, 3

Hepatic Causes

• Liver cirrhosis and hepatic disorders decrease protein synthesis, leading to decreased plasma oncotic pressure and increased systemic venous hypertension 1, 2
• This results in bilateral pitting edema and often ascites 4

Renal Causes

• Kidney disorders cause increased protein loss (nephrotic syndrome), decreased plasma oncotic pressure, and sodium/water retention 1, 2
• Reduced renal perfusion pressure from decreased arteriovenous pressure gradient contributes to fluid retention 2

Medication-Induced Edema

• Calcium channel blockers (especially dihydropyridines) are a leading pharmaceutical cause, more common in women, causing edema through increased capillary permeability 5, 1, 3
• NSAIDs cause edema through increased capillary permeability, sodium/water retention, and renal dysfunction 3
• Thiazolidinediones (TZDs) cause fluid retention, particularly when combined with insulin 5, 1
• Vasodilators and hormonal contraceptives/hormone replacement therapy can cause fluid retention 5, 3

Localized Causes (Unilateral or Asymmetric Edema)

Venous Pathology

• Chronic venous insufficiency is common in older patients, characterized by peripheral edema with hyperpigmentation, lipodermatosclerosis, and skin changes 1, 2
• Edema typically worsens with prolonged standing and improves with elevation 2
• Deep vein thrombosis (DVT) causes acute unilateral edema that may become chronic (post-thrombotic syndrome) 1, 2

Lymphatic Obstruction

• Lymphedema presents as brawny, nonpitting edema and can be primary or secondary to tumor, trauma, previous pelvic surgery, inguinal lymphadenectomy, or radiation therapy 6

Other Localized Causes

• Venous obstruction from pelvic tumors or compression 7
• Infection, trauma, or local inflammatory processes 7

Critical Distinguishing Features

Distribution Pattern

• Bilateral symmetric edema typically indicates systemic causes (cardiac, renal, hepatic disorders) 1, 2
• Unilateral or asymmetric edema more commonly indicates localized pathology (venous thrombosis, compression, lymphedema) 1, 2

Timing Pattern

• Worsening in the evening suggests venous insufficiency 1, 2
• Worsening in the morning suggests other systemic causes 1, 2

Edema Characteristics

• Pitting edema suggests cardiac, renal, hepatic, or venous causes 2, 4
• Non-pitting edema characterizes lymphedema 6

Diagnostic Approach Algorithm

Initial Assessment

1. Determine distribution: bilateral vs. unilateral 1
2. Assess for cardiac symptoms: dyspnea, orthopnea, paroxysmal nocturnal dyspnea 1, 3
3. Physical examination: evaluate for jugular venous distention, pulmonary rales, hepatojugular reflux, S3 gallop 1, 2
4. Medication review: identify calcium channel blockers, NSAIDs, TZDs, vasodilators 5, 1, 3

For Bilateral Edema

• Laboratory testing: BNP/NT-proBNP (to confirm/exclude heart failure), liver function tests, renal function tests, albumin 1, 2
• Evaluate for medication-induced causes before attributing to cardiac disease 1, 3

For Unilateral Edema

• Duplex ultrasonography to evaluate for DVT 6
• If negative but high clinical suspicion persists, consider magnetic resonance venography for pelvic or proximal thigh venous thrombosis 6
• Ankle-brachial index (ABI) to evaluate for peripheral arterial disease 1

For TZD-Related Edema

• Determine if CHF is present: assess for orthopnea, paroxysmal nocturnal dyspnea, unexplained cough/fatigue, jugular venous distention, S3 gallop, pulmonary rales 5
• Perform cardiac evaluation: ECG, echocardiogram, BNP measurement 5
• If CHF is absent, investigate other causes including venous insufficiency, nephrotic syndrome, or other medications 5

Common Pitfalls to Avoid

• Do not misattribute bilateral edema to cardiac causes without considering hepatic, renal, or medication-induced causes 1, 3
• Do not empirically prescribe diuretics without determining the underlying cause, as this can lead to severe electrolyte imbalances, volume depletion, and falls 3
• Do not assume bilateral venous insufficiency is common; when bilateral edema occurs, systemic causes should be investigated first 2
• Do not attribute edema to medications without first ruling out heart failure through physical examination and cardiac evaluation 3
• Incomplete evaluation for underlying systemic diseases can lead to delayed treatment and worse outcomes 1