What causes a swollen leg in a patient?

Why Would a Leg Be Swollen?

A swollen leg results from venous hypertension (most commonly from deep vein thrombosis or chronic venous insufficiency), lymphatic dysfunction, cardiac failure causing volume overload, or less commonly from arterial disease, medication effects, or systemic conditions affecting oncotic pressure. 1

Primary Mechanisms and Most Common Causes

The pathophysiology of leg swelling involves four key mechanisms that guide your diagnostic approach:

• Venous hypertension from valve incompetence or obstruction causes increased filtration pressure in capillaries, leading to fluid extravasation into tissues 2, 3
• Lymphatic dysfunction (primary or secondary) impairs fluid resorption from interstitial spaces 1, 3
• Volume overload from cardiac failure increases hydrostatic pressure throughout the venous system 1
• Decreased oncotic pressure from hypoproteinemia (liver or renal failure) reduces fluid reabsorption 1

Venous Causes (Most Common in Clinical Practice)

Acute Deep Vein Thrombosis

• Presents with sudden onset unilateral leg swelling, pain, and warmth 2
• Requires immediate compression ultrasound to exclude DVT, as this is life-threatening due to pulmonary embolism risk 2, 4
• The thrombosed vein causes outflow obstruction, leading to acute venous hypertension and rapid fluid accumulation 2

Chronic Venous Insufficiency

• Characterized by positional edema that worsens at end of day or with prolonged standing/walking and improves with rest or leg elevation 2, 5
• Symptoms include heaviness, aching, fatigue, itching, and cramping (often at night) 2
• Clinical signs progress from varicose veins and telangiectasias to hyperpigmentation, lipodermatosclerosis, and ultimately venous ulceration 2, 5
• Venous pressure increases dramatically to 80-90 mmHg when standing motionless, compared to 22 mmHg while walking, due to failed calf muscle pump function 2

Post-Thrombotic Syndrome

• Develops after DVT due to incomplete recanalization causing residual obstruction and valvular damage 2
• Presents with chronic pain, swelling, and skin changes that may appear without a symptom-free period after the initial DVT 2
• Venous claudication (bursting leg pain during exercise) suggests persistent obstruction of major venous confluence like iliofemoral or popliteal veins 2

Lymphatic Causes

• Primary lymphedema is hereditary, while secondary lymphedema results from obstruction (neoplasia, infection, surgery, radiation) 4
• Characterized by non-pitting edema that typically spares the foot initially but progresses proximally 4
• Affects approximately 140 million people worldwide but remains underdiagnosed 3
• Requires exclusion of malignancy as first step in acquired cases 4

Systemic and Other Causes

Cardiac Failure

• Causes bilateral dependent edema from volume overload and increased hydrostatic pressure 1
• Edema typically symmetric and accompanied by other signs of heart failure 1

Hypoproteinemia

• Results from liver cirrhosis, nephrotic syndrome, or severe malnutrition 1
• Decreased oncotic pressure allows fluid shift into interstitial space 1

Medication-Induced Edema

• Calcium channel blockers, NSAIDs, corticosteroids, and hormonal therapies commonly cause leg swelling 1
• Warfarin can cause purple toes syndrome (dark, purplish or mottled color of toes occurring 3-10 weeks after initiation), which may progress to gangrene requiring debridement or amputation 6

Lipedema (Important Differential)

• Bilateral symmetric lipohypertrophy with pressure sensitivity and susceptibility to hematomas 4
• Spares the feet (unlike lymphedema) and predominantly affects women 4
• Not true edema despite the name 1

Critical Diagnostic Distinctions

Venous vs. Arterial Disease

• Venous pain improves with elevation, while arterial rest pain worsens with elevation and improves with dependency 5
• Arterial ulcers are extremely painful and occur on toes/distal foot, while venous ulcers occur on medial malleolus and are less painful unless infected 2
• Always check pulses and consider ankle-brachial index (ABI) before applying compression therapy, as compression with ABI <0.6 can cause tissue necrosis 5

Acute vs. Chronic Presentation

• Acute unilateral swelling mandates immediate DVT exclusion with compression ultrasound and D-dimer testing 4
• Chronic bilateral swelling suggests systemic causes (cardiac, renal, hepatic) or bilateral venous/lymphatic disease 1
• Chronic unilateral swelling points to venous insufficiency, lymphedema, or lipedema 4

Common Pitfalls to Avoid

• Never apply compression therapy without first ruling out arterial insufficiency by checking pulses and ABI, as this can cause limb-threatening ischemia 5
• Do not assume all leg swelling with varicose veins is purely venous—always consider deep venous patency, as post-thrombotic syndrome can mimic primary venous insufficiency 7
• Recognize that superficial thrombophlebitis, particularly of the great saphenous vein, carries risk of pulmonary embolism and may indicate underlying malignancy or hypercoagulable state 7
• Do not miss systemic cholesterol microembolization presenting as purple toes syndrome, livedo reticularis, or acute limb pain, which can occur with anticoagulation therapy and requires warfarin discontinuation 6
• Avoid mistaking lipedema for lymphedema—lipedema spares the feet and has characteristic pressure sensitivity 4