unilateral pitting edema
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Unilateral Pitting Edema
Unilateral pitting edema — swelling of one limb that retains an indentation when pressed — is caused primarily by local rather than systemic pathology. Bilateral pitting edema points to cardiac, hepatic, or renal failure; unilateral presentation demands a different differential.
Key Causes
1. Deep Vein Thrombosis (DVT) ⭐ Most urgent
The most time-critical cause. Thrombus in the deep venous system obstructs venous outflow, producing unilateral leg swelling, pitting edema, erythema, warmth, and tenderness along the deep vein. The Homans sign (calf pain on passive dorsiflexion) is unreliable but may be present. Tachycardia and fever can occur.
Wells Score for DVT (each criterion = 1 point unless noted):
- Active cancer
- Paralysis/plaster immobilisation of lower limb
- Recently bedridden >3 days or major surgery within 12 weeks
- Tenderness along deep vein
- Entire leg swollen
- Unilateral calf swelling >3 cm (measured 10 cm below tibial tuberosity)
- Unilateral pitting edema
- Collateral superficial veins (non-varicose)
- Previous DVT
Score ≥2 = DVT likely → proceed to ultrasound. Score <2 = DVT unlikely → D-dimer.
DVT is also a key finding raising suspicion for pulmonary embolism (PE) — unilateral leg swelling is part of the PERC rule exclusion criteria and contributes to the Revised Geneva Score.
— Tintinalli's Emergency Medicine, Harrison's Principles 22E, Rockwood & Green
2. Cellulitis / Soft Tissue Infection
Bacterial infection of the dermis and subcutaneous tissue causes erythema, warmth, tenderness, and pitting edema localised to the infected region. Often confused with DVT. Fever, leukocytosis, and skin breakdown (wound, tinea pedis) provide clues. Streptococcal or staphylococcal organisms are most common. Recurrent cellulitis can itself damage lymphatics and eventually cause secondary lymphedema.
3. Chronic Venous Insufficiency (CVI)
Incompetent venous valves lead to venous hypertension and fluid extravasation. Typically bilateral, but can be predominantly unilateral early on or after unilateral injury/surgery. Features:
- Pitting edema (improves with leg elevation)
- Stasis dermatitis — hyperpigmentation, eczematous changes
- Superficial varicosities
- Lipodermatosclerosis
- Venous ulcers (typically around medial malleolus)
Unlike lymphedema, edema from CVI is softer and responds readily to elevation. — Fitzpatrick's Dermatology
4. Lymphedema
Impaired lymphatic drainage causes protein-rich fluid accumulation. Initially pitting, but progresses to non-pitting as fibrosis and subcutaneous fat deposition develop.
| Stage | Features |
|---|---|
| 0 (Ia) | Latent — no visible swelling despite impaired drainage |
| I | Pitting edema, improves with elevation |
| II | Pitting persists; late Stage II may not pit as fibrosis begins |
| III | Elephantiasis — non-pitting, trophic skin changes, warty overgrowths |
Key signs: Stemmer's sign (inability to tent skin at base of toes) and Kaposi-Stemmer sign. Late signs include "ski-jump" upturned toenails, papillomatosis, woody/fibrotic skin.
Primary lymphedema (rare): congenital (Milroy disease — FLT4/VEGFR3 mutation), lymphedema praecox (puberty onset, Meige disease — FOXC2 mutation), lymphedema tarda (>35 years).
Secondary lymphedema (common): post-surgical (axillary/inguinal node dissection for breast, cervical, prostate cancer — occurs in 13–22% after breast cancer surgery), irradiation, filariasis (most common worldwide cause), recurrent streptococcal lymphangitis, tumour infiltration.
— Harrison's Principles 22E, Fitzpatrick's Dermatology
5. Baker's Cyst Rupture
Rupture of a popliteal (Baker's) cyst causes sudden calf swelling and edema, mimicking DVT. Ultrasound distinguishes the two.
6. Other Causes
- Post-traumatic / musculoskeletal — fracture, haematoma, muscle tear
- Popliteal artery aneurysm with venous compression
- Superficial thrombophlebitis
- Extrinsic venous compression — tumour, lymphadenopathy, pregnancy-related iliac vein compression (left > right due to anatomy — May-Thurner syndrome)
- Lipedema — bilateral fat deposition, usually sparing the feet; predominantly in women; not true pitting edema
- Myxedema — usually non-pitting; from hypothyroidism
- Reflex sympathetic dystrophy / CRPS
Clinical Approach
| Step | Action |
|---|---|
| History | Onset, travel/immobilisation, surgery, malignancy, trauma, skin breakdown |
| Examine | Measure calf circumference bilaterally (>3 cm asymmetry = significant), skin colour/temperature, tenderness over deep vein, varicosities |
| Pre-test probability | Calculate Wells DVT Score |
| Investigations | Compression ultrasound (Doppler) is the first-line imaging for DVT; D-dimer if low pre-test probability; CBC, CRP if cellulitis suspected |
| If DVT excluded | Consider duplex for CVI, MRI/CT for lymphedema or pelvic mass, lymphoscintigraphy if primary lymphedema suspected |
Key Distinguishing Features
| Feature | DVT | Cellulitis | Lymphedema | CVI |
|---|---|---|---|---|
| Pain | Variable | Yes (tender) | Usually painless | Aching |
| Skin | Normal/blue | Red, hot | Thickened, fibrotic | Pigmented, stasis dermatitis |
| Pitting | Yes | Yes (early) | Early yes, late no | Yes |
| Fever | Sometimes | Often | No | No |
| Stemmer's sign | Negative | Negative | Positive | Negative |
| Elevated leg | Partial relief | No change | Mild relief (early) | Good relief |
The most urgent diagnosis to exclude is always DVT, given the risk of pulmonary embolism. Compression ultrasound should be obtained promptly when DVT is suspected.
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