Dermatology >
Cellulitis

“Acute bacterial infection of the dermis and subcutaneous tissue”

Risk Factors
  • Skin trauma
  • Ulceration
  • Obesity
  • IV drug use (unusual organism)
  • Chronic lymphoedemats
Aetiology
  • Flora colonising skin e.g commonly Strep. pyogenes and Staph. aureus gain entry e.g. through breaks in skin, burns, insect bites, surgical incisions and IV catheters.
  • S. aureus cellulitis spreads from a central localised infection e.g. splinter
  • S. pyogenes cellulitis spreads rapidly and diffusely, associated with lymphangitis and fever.
  • Recurrent streptococcal cellulitis can be seen in the lower extremities in conjunction with chronic venous stasis or saphenous vein harvest for CABG
Pathophysiology
  • Disruption in cutaneous barrier -> invasion of micro-organisms to the dermal and subcutaneous tissue 
Clinical Presentation
  • Pain, heat, swelling and erythema, most commonly on the lower limb. Lacks demarcation from uninvolved skin. Formation of blisters and bullae. Fever, malaise, nausea and rigors may accompany the skin changes
Investigations
  • Blood culture, swab for culture if open wound, and sensitivity tests, especially in cases with unusual organisms.
  • Diagnosis mainly based on the clinical setting and morphological features of the lesion
Management
  • Eron classification used for management decisions (Class I->IV)
    • Class I: no signs of systemic toxicity or uncontrolled comorbidities
    • Management of uncomplicated cellulitis (Class I): appropriate antibiotic prescription, analgesia, adequate fluid, elevation of affected area to reduce oedema if applicable, advice on when to seek immediate medical review. Management of underlying risk factors
  • Hospital admission may be required for class II cellulitis and is necessary for class III-IV cellulitis
    • Class II: systemically unwell or systemically well with comorbidity e.g. peripheral arterial disease
    • Class III: significant systemic upset, unstable comorbidities which may interfere with treatment, or a limb-threatening infection due to vascular compromise
    • Class IV: sepsis or severe life-threatening infection e.g. necrotising fasciitis
Complications
  • Necrotising fasciitis
  • Sepsis
  • Persistent leg ulceration
  • Recurrent cellulitis

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