Cellulitis

Info & Pathophysiology

Source: OpenI (NLM)

What is it?

Deep dermal infection that can extend to subcutaneous adipose tissue; primarily affects lower extremities due to diminished blood circulation

Indolent and slow onset

Risk Factors: obesity, immunosuppression, chronic vascular insufficiency (especially in recurrent cellulitis), lymphatic insufficiency, other skin afflictions (e.g. tinea infections), animal bites

Clinical presentation: poorly demarcated erythematous raised rash with palpation tenderness; no abscess or purulent discharge; can see regional lymphadenopathy but generally localized symptoms; can become scaly during recovery process


Pathophysiology:

  • Primarily s. aureus infection (purulent cellulitis) or beta-hemolytic streptococci or MSSA (nonpurulent cellulitis)
  • Infection can also be caused by:
    • Freshwater environment: Aeromonas hydrophila
    • Seawater: Vibrio vulnificus
    • Hot tub: Pseudomonas aeruginosa; associated with puncture wounds in foot/hand
    • Fish/poultry handling: Erysipelothrix
  • Bacterial colonization induces epidermal immune response →production of antimicrobial peptides and keratinocyte proliferation → GABHS can produce virulence factors (pyrogenic exotoxins A, B, C, F)

Differential Diagnosis: Erysipelas vs. Cellulitis

Cellulitis

Source: OpenI (NLM)

Infectious agent: Strep and S.aureus in equal incidence

Infection depth: infection extends all the way to deeper dermis and subcutaneous adipose tissue

Course of onset: indolent onset, slow development over a few days

Lesion characteristics: can be purulent (s.aureus) or nonpurulent (beta-hemolytic streptococci or MSSA), poor demarcation, no abscess or purulent discharge

Erysipelas

Source: OpenI (NLM)

Infectious agent: most common agent is Group A Strep

Infection depth: limited to upper dermis and superficial lymphatics

Course of onset: acute and abrupt onset

Lesion characteristics: always nonpurulent, clear demarcation and often raised

If involves ear, will present with Milian’s Ear Sign

Similarities

  • Both are bacterial skin infections
  • Both are erythematous, edematous, warm/hot to touch
  • Almost always unilateral in lower extremities
  • Similar risk factors (see above)
  • Diagnosis is mostly clinical

Treatment

Oral antibiotic therapy max 5 day treatment; good progression if treated within 48h (before infection further invades subcutaneous tissue)

Nonpurulent cellulitis

  • Cephalexin/PO or cefazolin/IV
  • IF MSSA: mupirocin, retapamulin

Purulent cellulitis

  • Need to cover for MRSA: clindamycin, tetracyclines, vancomycin

Hydration, cold compresses or other compression therapy to reduce swelling

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