Cellulitis vs Necrotizing fasciitis
How to tell Cellulitis and Necrotizing fasciitis apart when a board question makes them look alike.
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Pain out of proportion with rapid progression is the bedside discriminator for necrotizing fasciitis.
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Localized warm erythema and tenderness with gradual progression and no deep tissue crepitus usually indicates cellulitis.
Severe pain out of proportion, rapidly advancing edema, bullae, skin anesthesia, or crepitus suggests necrotizing fasciitis.
Cellulitis is superficial dermal and subcutaneous bacterial infection, usually streptococcal or staphylococcal.
Necrotizing fasciitis is a deep fascial infection with microvascular thrombosis and rapid tissue necrosis.
Cellulitis may have mild leukocytosis and inflammatory marker elevation; ultrasound can exclude abscess when fluctuance is unclear.
Necrotizing fasciitis often shows leukocytosis above 15,000/uL, CRP above 150 mg/L, hyponatremia, elevated creatine kinase, and CT or MRI with fascial gas or deep fascial edema.
The trap
Early necrotizing fasciitis can look like uncomplicated cellulitis, so treatment with oral antibiotics alone causes dangerous delay. Disproportionate pain, systemic toxicity, or crepitus should trigger immediate surgical exploration.
The repair move
Next best step: call surgery emergently for immediate operative debridement while starting broad-spectrum IV antibiotics, such as vancomycin plus piperacillin-tazobactam plus clindamycin. Begin aggressive sepsis resuscitation with 30 mL/kg crystalloid and repeat debridement every 24 to 48 hours until no necrotic tissue remains.
Try a free question
CoreA 49-year-old woman has progressive left calf erythema for 2 days after a skin abrasion. BP 124/78 mm Hg, HR 88/min, temp 38.0 C. The area is warm and tender without bullae or crepitus, and pain is proportional to exam. What is the most likely diagnosis?
Show answer and explanation
Answer: A. Cellulitis. Gradual superficial erythema and tenderness without deep tissue warning signs is most consistent with cellulitis.
Why the other choices are tempting
- B. Necrotizing fasciitis is less likely without disproportionate pain, rapid shock, bullae, or crepitus.
- C. DVT causes swelling and pain but usually lacks warm erythematous infectious skin changes and fever.
- D. Contact dermatitis is pruritic and not typically febrile with spreading tenderness.
- E. Pyoderma gangrenosum is an ulcerative neutrophilic dermatosis, not this acute spreading infection.
Flashcards
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Which bedside clue most urgently distinguishes necrotizing fasciitis from cellulitis?
Pain out of proportion to visible skin findings is the most urgent clue for necrotizing fasciitis.
What progression pattern is typical for uncomplicated cellulitis?
Cellulitis typically progresses gradually with localized erythema, warmth, and tenderness without deep tissue signs.
Quick answers
What is the fastest way to tell Cellulitis from Necrotizing fasciitis?
Pain out of proportion with rapid progression is the bedside discriminator for necrotizing fasciitis.
What is the key clue for Cellulitis?
Localized warm erythema and tenderness with gradual progression and no deep tissue crepitus usually indicates cellulitis.
What is the key clue for Necrotizing fasciitis?
Severe pain out of proportion, rapidly advancing edema, bullae, skin anesthesia, or crepitus suggests necrotizing fasciitis.
What is the common trap with Cellulitis vs Necrotizing fasciitis?
Early necrotizing fasciitis can look like uncomplicated cellulitis, so treatment with oral antibiotics alone causes dangerous delay. Disproportionate pain, systemic toxicity, or crepitus should trigger immediate surgical exploration.