Is infection synonymous with cellulitis?

No, Infection is Not Technically Synonymous with Cellulitis

Infection is not synonymous with cellulitis; cellulitis is a specific type of skin and soft tissue infection with distinct clinical and pathological characteristics. 1

Definition and Differentiation

Cellulitis refers specifically to a diffuse, spreading bacterial infection of the dermis and subcutaneous tissue with the following characteristics:

• Affects deeper dermis and subcutaneous fat (unlike erysipelas which involves upper dermis)
• Presents with rapidly spreading areas of erythema, swelling, tenderness, and warmth
• Often accompanied by lymphangitis and regional lymph node inflammation
• May present with "peau d'orange" appearance due to superficial cutaneous edema 1

Important Distinction

The term "cellulitis" should not be used for:

• Cutaneous inflammation associated with collections of pus
• Septic bursitis
• Furuncles or skin abscesses
• Necrotizing fasciitis
• Septic arthritis
• Osteomyelitis 1

For example, when redness surrounds a suppurative focus like an infected bursa, the correct terminology is "septic bursitis with surrounding inflammation" rather than "septic bursitis with surrounding cellulitis." 1

Clinical Implications of This Distinction

This differentiation is clinically crucial because:

1. Treatment approach differs:

   • Cellulitis primarily requires antimicrobial therapy
   • Purulent collections primarily require drainage, with antibiotics playing a secondary role 1

2. Causative organisms differ:

   • Cellulitis is predominantly caused by streptococci (especially Group A) and less commonly by Staphylococcus aureus
   • Other infections may have different microbial profiles 1

Types of Skin and Soft Tissue Infections

The broader category of skin and soft tissue infections includes:

• Superficial infections:

  • Impetigo (superficial epidermal)
  • Erysipelas (upper dermis)
  • Cellulitis (deeper dermis and subcutaneous tissue)
  • Superficial abscesses 1

• Deep tissue infections:

  • Necrotizing fasciitis
  • Myonecrosis
  • Deep abscesses

Diagnostic Approach

Cellulitis is primarily a clinical diagnosis based on physical examination findings:

• Erythema
• Tenderness
• Induration
• Warmth
• Possible systemic symptoms (fever, tachycardia, leukocytosis) 1

Blood cultures, tissue aspirates, or skin biopsies are generally unnecessary for typical cases but may be considered in patients with:

• Malignancy
• Severe systemic features
• Unusual predisposing factors (immersion injury, animal bites)
• Immunocompromised states 1

Treatment Considerations

Treatment should be directed at the most likely causative organisms:

• For typical cellulitis: antibiotics active against streptococci (penicillin, amoxicillin, cephalexin)
• For suspected MRSA involvement: consider vancomycin, daptomycin, linezolid, or oral options like clindamycin, doxycycline, or SMX-TMP 1

For simple abscesses or boils, incision and drainage is the primary treatment, and antibiotics are generally not needed 1.

Common Pitfalls

1. Misdiagnosis: Venous insufficiency, eczema, deep vein thrombosis, and gout are frequently mistaken for cellulitis 2

2. Inappropriate terminology: Using "cellulitis" as a catch-all term for any skin infection or inflammation leads to improper treatment approaches

3. Overlooking underlying causes: Failure to address predisposing conditions (diabetes, obesity, venous insufficiency) may lead to recurrent infections 2

4. Inappropriate antibiotic selection: Using broad-spectrum antibiotics when narrow-spectrum would suffice, or failing to cover the most likely pathogens

Remember that proper identification and classification of skin infections is essential for appropriate management and optimal patient outcomes.