What is the diagnosis and treatment for a patient presenting with a 3-day history of a swollen lower right leg and foot with erythema and tenderness, without fever or systemic symptoms?

Differential Diagnosis and Management

The most likely diagnosis is cellulitis, though deep vein thrombosis (DVT) must be urgently excluded given the unilateral leg swelling, erythema, and tenderness. 1, 2

Immediate Diagnostic Approach

Clinical Assessment for DVT vs. Cellulitis

Calculate the Wells score immediately to stratify DVT probability before proceeding with further testing. 1 The Wells score assigns points for:

• Active cancer (1 point) 1
• Recent immobilization or surgery (1 point) 1
• Localized tenderness along deep venous distribution (1 point) 1
• Entire leg swelling (1 point) 1
• Calf swelling ≥3 cm compared to asymptomatic side (1 point) 1
• Pitting edema confined to symptomatic leg (1 point) 1
• Collateral superficial veins (1 point) 1
• Previously documented DVT (1 point) 1
• Alternative diagnosis at least as likely as DVT (-2 points) 1

Risk Stratification Algorithm

If Wells score <2 (DVT "unlikely"): Obtain high-sensitivity D-dimer first. 1

• If D-dimer negative: DVT excluded, proceed with cellulitis evaluation 1
• If D-dimer positive: Perform complete duplex ultrasound (CDUS) 1

If Wells score ≥2 (DVT "likely"): Proceed directly to CDUS without D-dimer. 1

Ultrasound Protocol

Complete duplex ultrasound from inguinal ligament to ankle (including posterior tibial and peroneal veins) is mandatory—limited protocols are inadequate. 1 The examination must include:

• Compression at 2-cm intervals throughout the deep venous system 1
• Bilateral common femoral vein spectral Doppler waveforms 1
• Popliteal spectral Doppler 1
• Color Doppler imaging 1

Critical pitfall: Limited protocols that exclude calf veins require repeat scanning in 5-7 days and miss clinically significant thrombi. 1

Cellulitis Diagnosis

If DVT is excluded, diagnose cellulitis based on the presence of at least 2 classic inflammatory signs: erythema, warmth, tenderness, pain, or induration. 1 This patient meets criteria with erythema, tenderness, and swelling. 1

Severity Classification

Classify infection severity to guide treatment intensity: 1

• Mild: Erythema 0.5-2 cm, involving only skin/subcutaneous tissue, no systemic signs 1
• Moderate: Erythema >2 cm OR deeper tissue involvement (abscess, fasciitis), no systemic signs 1
• Severe: Any local infection PLUS systemic inflammatory response syndrome (SIRS): temperature >38°C or <36°C, heart rate >90, respiratory rate >20, WBC >12,000 or <4,000 1

This patient appears to have mild-to-moderate cellulitis given the 3-day history without fever or systemic symptoms. 1

Critical Exclusions

Actively exclude alternative inflammatory conditions that mimic cellulitis: 1

• Trauma 1
• Gout 1
• Acute Charcot neuro-osteoarthropathy (in diabetics) 1
• Fracture 1
• Venous stasis 1

Treatment Protocol

For Mild-to-Moderate Cellulitis (No Systemic Symptoms)

Initiate empirical oral antibiotics targeting Gram-positive organisms, particularly staphylococci and streptococci. 3 Common regimens include:

• Cephalexin 500 mg four times daily 3
• Dicloxacillin 500 mg four times daily 3
• If MRSA risk factors present: Add trimethoprim-sulfamethoxazole or doxycycline 3

Treatment duration: 5-10 days for uncomplicated cellulitis, extending based on clinical response. 3

Monitoring and Follow-up

Reassess within 24-48 hours to confirm clinical improvement: 3

• Decreasing erythema and tenderness indicate appropriate therapy 3
• Mark the border of erythema with a pen to objectively track progression or regression 2
• Worsening symptoms or systemic signs require immediate escalation to IV antibiotics and hospitalization 1, 3

Special Considerations for Diabetic Patients

If the patient has diabetes, perform comprehensive three-level assessment: 1, 3

1. Patient level: Check temperature, vital signs, glucose control, renal function 3
2. Limb level: Assess vascular status (pedal pulses, ABI), test protective sensation with 10-g monofilament 1, 3
3. Wound level: Probe for deeper involvement, obtain wound cultures if present 1, 3

Diabetic patients require more aggressive management as inflammatory markers may be absent even with severe infection. 1 Consider baseline CRP and ESR, as elevated levels predict worse outcomes and guide treatment duration. 1, 3

Red Flags Requiring Urgent Intervention

Seek immediate surgical consultation if any of the following develop: 1

• Rapid progression of infection 1
• Crepitus or tissue gas 1
• Bullae, especially hemorrhagic 1
• Pain out of proportion to findings 1
• New neurologic deficits 1
• Failure to improve with appropriate therapy 1

Common Pitfalls

Do not rely solely on absence of fever or leukocytosis to exclude serious infection—up to 50% of severe infections lack these findings. 1

Do not use superficial wound swabs for culture—they are unreliable and contaminated with colonizing flora. 3

Do not accept limited ultrasound protocols that exclude calf veins, as they miss significant DVT and require repeat imaging. 1