Cellulitis vs Erysipelas and necrotizing fasciitis
How to tell Cellulitis and Erysipelas and necrotizing fasciitis apart when a board question makes them look alike.
Cellulitis is poorly demarcated deeper infection; erysipelas is raised sharply demarcated superficial infection; nec fasc is toxic pain-out-of-proportion fascial infection.
Side by side
Cellulitis causes deeper dermal/subcutaneous infection with warmth, erythema, swelling, tenderness, and poorly demarcated borders.
Erysipelas is superficial sharply demarcated raised infection; necrotizing fasciitis causes pain out of proportion, toxicity, bullae, crepitus, and fascial necrosis.
Bacteria infect deeper dermis and subcutaneous tissue, often after barrier disruption.
Erysipelas involves upper dermis and lymphatics; necrotizing fasciitis spreads along fascia with thrombosis and tissue death.
Poorly demarcated tender erythema supports cellulitis.
Raised sharp borders support erysipelas; severe pain, gas, bullae, and systemic toxicity support necrotizing fasciitis.
The trap
Red warm skin overlaps, but border sharpness, pain severity, toxicity, and crepitus separate them.
The repair move
For red, warm skin infection, judge depth, border, toxicity, and pain in three steps: (1) sharply demarcated, raised, well-defined border with bright red surface equals ERYSIPELAS (superficial upper-dermis infection of lymphatics, usually group A Strep, often high fever; treat with penicillin or amoxicillin); (2) poorly demarcated, deeper infection without sharp border, with warmth and edema equals CELLULITIS (deeper dermis and subcutaneous tissue; non-purulent cellulitis is usually group A Strep treat with cephalexin or dicloxacillin; purulent cellulitis with abscess is more often S. aureus including MRSA treat with TMP-SMX, doxycycline, clindamycin); (3) SEVERE PAIN OUT OF PROPORTION to exam findings, rapid progression, systemic toxicity, crepitus on palpation, skin necrosis, bullae, or anesthesia equals NECROTIZING FASCIITIS (polymicrobial Type 1 in diabetics, or monomicrobial Type 2 from group A Strep with TSS, or Clostridium perfringens with gas gangrene; SURGICAL EMERGENCY needing urgent debridement plus broad-spectrum antibiotics like piperacillin-tazobactam plus vancomycin plus clindamycin; LRINEC score helps stratify risk but does NOT exclude diagnosis if clinical suspicion is high).
Try a free question
CoreA 56-year-old woman with venous insufficiency has 2 days of progressive warm, erythematous, swollen, tender lower leg with poorly demarcated borders. There is no skin break or systemic toxicity. Temp 38.0 C. WBC 13,200/uL. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Cellulitis. Cellulitis is a deeper soft tissue bacterial infection with poorly demarcated erythema, warmth, swelling, and tenderness; usually due to Staphylococcus aureus or Streptococcus pyogenes; treatment is cephalexin or dicloxacillin.
Why the other choices are tempting
- B. Erysipelas is a more superficial infection with raised, sharply demarcated borders and bright red color.
- C. Necrotizing fasciitis has pain out of proportion, rapid progression, hemorrhagic bullae, crepitus, and systemic toxicity.
- D. Stasis dermatitis is chronic bilateral lower leg edema with hyperpigmentation but lacks acute infection.
- E. DVT has unilateral swelling and tenderness with positive ultrasound but lacks the prominent erythema and warmth.
Flashcards
Tap a card to flip it.
What border supports erysipelas?
Sharply demarcated raised borders support erysipelas.
What pain clue supports necrotizing fasciitis?
Pain out of proportion supports necrotizing fasciitis.
Quick answers
What is the fastest way to tell Cellulitis from Erysipelas and necrotizing fasciitis?
Cellulitis is poorly demarcated deeper infection; erysipelas is raised sharply demarcated superficial infection; nec fasc is toxic pain-out-of-proportion fascial infection.
What is the key clue for Cellulitis?
Cellulitis causes deeper dermal/subcutaneous infection with warmth, erythema, swelling, tenderness, and poorly demarcated borders.
What is the key clue for Erysipelas and necrotizing fasciitis?
Erysipelas is superficial sharply demarcated raised infection; necrotizing fasciitis causes pain out of proportion, toxicity, bullae, crepitus, and fascial necrosis.
What is the common trap with Cellulitis vs Erysipelas and necrotizing fasciitis?
Red warm skin overlaps, but border sharpness, pain severity, toxicity, and crepitus separate them.