Cellulitis vs Necrotizing Fasciitis
Cellulitis and Necrotizing Fasciitis are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.
Cellulitis vs Necrotizing Fasciitis at a glance
- Cellulitis: Acute bacterial infection of the dermis and subcutaneous tissue, most often caused by beta-hemolytic streptococci or Staphylococcus aureus.
- Necrotizing Fasciitis: Rapidly progressive, life-threatening deep soft tissue infection requiring emergent surgical debridement and broad-spectrum antibiotics.
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Side-by-side comparison
| Feature | Cellulitis | Necrotizing Fasciitis |
|---|---|---|
| At a glance | Acute bacterial infection of the dermis and subcutaneous tissue, most often caused by beta-hemolytic streptococci or Staphylococcus aureus. | Rapidly progressive, life-threatening deep soft tissue infection requiring emergent surgical debridement and broad-spectrum antibiotics. |
| Classic presentation | Unilateral lower-leg cellulitis is extremely common; bilateral lower-leg 'cellulitis' is almost never cellulitis — consider stasis dermatitis,… | Patient with severe pain disproportionate to exam, rapidly spreading edema, hemorrhagic bullae, and systemic toxicity — emergency surgical exploration… |
| Workup / key labs | Clinical diagnosis. IDSA stratifies into mild, moderate, severe and purulent vs non-purulent for treatment selection.; CBC, BMP, lactate if systemic toxicity;… | Clinical diagnosis confirmed at surgical exploration: gray, necrotic, easily dissected fascia ('finger test'); lack of bleeding; foul-smelling discharge.… |
| Imaging | Bedside ultrasound to differentiate cellulitis (cobblestoning) from abscess (anechoic collection); Plain films for foreign body, soft tissue gas (necrotizing… | Plain films may show soft tissue gas (not always present); CT with contrast (most useful): fascial thickening, gas, fluid tracking along fascia, lack of… |
| First-line treatment | Non-purulent cellulitis (likely beta-hemolytic strep):; • Mild outpatient: oral beta-lactam — cephalexin 500 mg PO QID, dicloxacillin 500 mg PO QID, or… | Emergent surgical debridement is the cornerstone — every hour of delay increases mortality (Wong 2003); Broad-spectrum empiric antibiotics immediately:; •… |
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