What is cellulitis described as?

Cellulitis Description and Characteristics

Cellulitis is a diffuse, superficial, spreading bacterial infection involving the deeper dermis and subcutaneous tissue that presents with rapidly spreading areas of erythema, swelling, tenderness, and warmth. 1

Clinical Presentation

Cellulitis typically manifests with:

• Rapidly spreading areas of erythema (redness)
• Swelling and edema
• Tenderness and pain
• Warmth over the affected area
• Orange peel appearance (peau d'orange) due to superficial cutaneous edema surrounding hair follicles 2
• Possible development of vesicles, bullae, and cutaneous hemorrhage (petechiae or ecchymoses) 2
• Sometimes accompanied by lymphangitis and inflammation of regional lymph nodes 2
• Systemic manifestations may include fever, tachycardia, confusion, hypotension, and leukocytosis 2

Anatomical Distinction

It's important to understand that:

• Cellulitis involves the deeper dermis and subcutaneous fat
• This distinguishes it from erysipelas, which affects only the upper dermis and superficial lymphatics 2, 1
• The term "cellulitis" is not appropriate for cutaneous inflammation associated with collections of pus (such as septic bursitis, furuncles, or skin abscesses) 2

Common Locations and Risk Factors

Cellulitis can occur anywhere on the body but most commonly affects:

• Lower extremities
• Areas with predisposing factors such as:
  • Obesity
  • Previous cutaneous damage
  • Edema from venous insufficiency or lymphatic obstruction
  • Trauma
  • Preexisting skin infections
  • Fissured toe webs (often harboring streptococci) 2
  • Inflammatory dermatoses 1

Causative Organisms

The most common causative organisms are:

• β-hemolytic streptococci (most frequent), particularly group A, but also groups B, C, or G 2, 1
• Staphylococcus aureus (less frequent, often associated with previous penetrating trauma) 2, 1
• Other organisms in special circumstances:
  • Pasteurella species (cat or dog bites)
  • Aeromonas hydrophila (freshwater exposure)
  • Vibrio species (saltwater exposure) 2

Diagnostic Considerations

Cellulitis is primarily a clinical diagnosis:

• Blood cultures are positive in only about 5% of cases 1
• Cultures of blood, tissue aspirates, or skin biopsies are unnecessary for typical cases 2
• Blood cultures should be obtained for patients with:
  • Malignancy
  • Severe systemic features
  • Unusual predisposing factors 2

Differential Diagnosis

Cellulitis must be distinguished from conditions that may appear similar:

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

Treatment Approach

For typical cases of cellulitis:

• Antibiotic therapy should target streptococci
• Suitable oral antibiotics include penicillin, amoxicillin, amoxicillin-clavulanate, dicloxacillin, cephalexin, or clindamycin 2
• A 5-day course is as effective as a 10-day course if clinical improvement occurs by day 5 2
• MRSA is an unusual cause of typical cellulitis, and specific coverage is generally unnecessary unless there are risk factors 2, 4

Common Pitfalls

• Failure to distinguish cellulitis from purulent collections that require drainage
• Overdiagnosis of cellulitis in cases of non-infectious inflammatory conditions
• Overuse of broad-spectrum antibiotics when narrower-spectrum options would be effective
• Failure to address predisposing factors, which is essential for preventing recurrence 1

Remember that cellulitis requires antimicrobial therapy as the primary treatment, whereas purulent collections require drainage as the major component of management, with antimicrobials playing a subsidiary role 2.