How do you assess for cellulitis?

Assessment for Cellulitis

Cellulitis should be diagnosed clinically based on the presence of purulent secretions (pus) or at least 2 of the cardinal manifestations of inflammation: redness, warmth, swelling/induration, and pain/tenderness. 1

Clinical Evaluation

Physical Examination

• Look for cardinal signs of inflammation:
  • Erythema (redness)
  • Warmth
  • Swelling or induration
  • Pain or tenderness
• Assess for purulent drainage
• Measure and document:
  • Size and extent of erythema
  • Extent of surrounding cellulitis
  • Quality and quantity of any drainage (color and odor) 1

Wound Assessment (if present)

• Use a sterile, blunt metal probe to:
  • Measure depth and extent of any wound
  • Check for foreign bodies
  • Assess for soft-tissue abscesses
  • Identify communication with joint cavities or tendon sheaths
  • Check for palpable bone (bone touched with a probe has a characteristic stony feel) 1

Differential Diagnosis

Many conditions can mimic cellulitis, with diagnostic accuracy for cellulitis being only approximately 33% 2. Common mimics include:

• Venous stasis dermatitis
• Contact dermatitis
• Deep vein thrombosis
• Panniculitis
• Eczema
• Lymphedema
• Erythema migrans 3, 4

Diagnostic Testing

Microbiology

• Obtain specimens for culture before initiating antibiotic therapy when possible 1
• Tissue samples provide more accurate culture results than superficial swab specimens 1
• Note: The majority of cellulitis cases are nonculturable, making identification of causative bacteria difficult 5
• When organisms are identified (approximately 15% of cases), most are due to β-hemolytic Streptococcus and Staphylococcus aureus 5

Imaging

• Ultrasonography (especially high resolution) and CT scanning may help detect deep soft-tissue abscesses or sinus tracts 1
• Plain radiographs and MRIs are best for detecting bone involvement 1
• MRI can provide anatomic information about sinus tracts, abscesses, or muscle involvement 1
• Nuclear medicine scans may be useful in some cases but are generally less specific than MRI 1

Assessment Algorithm

1. Initial Assessment:

   • Evaluate for purulent drainage or at least 2 cardinal signs of inflammation
   • Document extent and characteristics of affected area

2. Determine if abscess is present:

   • Fluctuance
   • Pointing
   • Ultrasonography if uncertain

3. Assess for complications/deeper infection:

   • Probe any wounds for depth and bone contact
   • Check for systemic signs of infection (fever, tachycardia)
   • Consider imaging for suspected deep tissue involvement

4. Rule out mimics:

   • Consider vascular assessment (Doppler studies, ABI) if vascular etiology suspected
   • Assess for predisposing conditions (diabetes, venous insufficiency)

Special Considerations

• Diabetic patients require thorough assessment for peripheral neuropathy and vascular disease:

  • Test for loss of protective sensation using 10-g nylon monofilament
  • Consider vascular assessment with ABI, ankle blood pressure, or TcpO2 1

• Recurrent cellulitis requires investigation of predisposing factors that can be addressed to prevent recurrence 5

• MRSA risk assessment should be performed in patients with:

  • Previous MRSA infection or colonization
  • Injection drug use
  • Systemic inflammatory response syndrome
  • Failed initial antibiotic treatment
  • Immunocompromised status 6

Common Pitfalls to Avoid

1. Failing to consider non-infectious mimics of cellulitis
2. Not performing incision and drainage when an abscess is present
3. Neglecting to obtain appropriate cultures before starting antibiotics
4. Missing deeper infections (osteomyelitis, necrotizing fasciitis) that may present with cellulitis-like symptoms
5. Overlooking predisposing factors that need correction to prevent recurrence

Remember that cellulitis is primarily a clinical diagnosis based on history and physical examination, as there are no definitive diagnostic tests 5, 7. Careful assessment and consideration of differential diagnoses are essential for accurate diagnosis and appropriate management.