What are the diagnostic approaches and treatment options for cellulitis?

Diagnostic Approaches and Treatment Options for Cellulitis

Blood cultures and tissue cultures are unnecessary for typical cases of cellulitis, but should be obtained for patients with malignancy, severe systemic features, unusual predisposing factors, neutropenia, or severe cell-mediated immunodeficiency. 1, 2

Diagnostic Approach

Clinical Diagnosis

• Cellulitis is primarily diagnosed based on clinical presentation 3:
  • Expanding erythema
  • Warmth
  • Tenderness
  • Swelling
  • Superficial cutaneous edema may create "orange peel" appearance (peau d'orange) 1

When to Obtain Cultures

• Blood cultures indicated for:
  • Patients with malignancy
  • Severe systemic features (high fever, hypotension)
  • Unusual predisposing factors (immersion injury, animal bites)
  • Neutropenia
  • Severe cell-mediated immunodeficiency 1, 2

Laboratory Assessment

For patients with signs of systemic toxicity, obtain:

• Blood cultures
• Complete blood count with differential
• Creatinine, bicarbonate levels
• Creatine phosphokinase
• C-reactive protein 1

Imaging

• Point-of-care ultrasound can help differentiate cellulitis from abscess in unclear cases 4
• Consider deeper imaging if concerned about necrotizing infection or osteomyelitis

Warning Signs of Severe Infection

Consider surgical consultation if any of these are present:

1. Pain disproportionate to physical findings
2. Violaceous bullae
3. Cutaneous hemorrhage
4. Skin sloughing
5. Skin anesthesia
6. Rapid progression
7. Gas in tissue 1

Treatment Algorithm

First-Line Therapy for Typical Cellulitis

• Outpatient (mild cases):

  • Beta-lactam antibiotics targeting streptococci:
    • Cephalexin: 500 mg 3-4 times daily
    • Dicloxacillin: 500 mg four times daily
    • Amoxicillin-clavulanate: 875/125 mg twice daily
    • Clindamycin: 300-450 mg three times daily (for penicillin-allergic patients) 2

• Inpatient (moderate-severe cases):

  • Cefazolin: 1-2g IV every 8 hours
  • Oxacillin: 1-2g IV every 4-6 hours 2

Duration of Therapy

• 5-day course is as effective as 10-day course if clinical improvement occurs by day 5 1, 2
• Reassess within 48-72 hours of initiating therapy 2

When to Consider MRSA Coverage

Add MRSA coverage only in specific situations:

• Cellulitis associated with penetrating trauma
• History of illicit drug use
• Purulent drainage
• Concurrent evidence of MRSA infection elsewhere
• Failure to respond to beta-lactam therapy within 48-72 hours 1, 2

MRSA Treatment Options

• IV options:

  • Vancomycin: 15-20 mg/kg IV every 8-12 hours
  • Daptomycin: 4-6 mg/kg IV daily
  • Linezolid: 600 mg IV every 12 hours
  • Telavancin: 10 mg/kg IV once daily 2

• Oral options:

  • Clindamycin: 300-450 mg three times daily
  • TMP-SMX
  • Doxycycline plus a beta-lactam 2

Supportive Care

• Elevate affected area to promote drainage of edema 1, 2
• Consider systemic corticosteroids (prednisone 40 mg daily for 7 days) in non-diabetic adults 1, 2
• Address predisposing conditions (tinea pedis, trauma, venous eczema) 1, 2

Common Pitfalls and Caveats

1. Misdiagnosis: Cellulitis is frequently misdiagnosed, with conditions like venous stasis dermatitis, contact dermatitis, and lymphedema often mistaken for cellulitis 5

2. Unnecessary MRSA coverage: MRSA is an unusual cause of typical cellulitis. A study showed that treatment with beta-lactams was successful in 96% of patients with cellulitis, suggesting MRSA coverage is usually unnecessary 1

3. Overlooking predisposing factors: Failure to address underlying conditions can lead to recurrence 2

4. Inadequate drainage: Antibiotics alone are insufficient for purulent collections; surgical drainage is essential 2

5. Premature discontinuation of antibiotics: Patients should complete the full course even if symptoms improve quickly 2

6. Failure to recognize necrotizing infections: Signs often appear late in the course of necrotizing infections, making emergent surgical evaluation crucial 1

7. Recurrent cellulitis: Annual recurrence rates are about 8-20%, especially involving the legs 1. Consider prophylaxis for frequent recurrences 6