# Cellulitis, Erysipelas and Necrotising Fasciitis > Cellulitis, erysipelas and necrotising fasciitis for NEET-PG Medicine, with streptococcal versus staphylococcal skin infection, LRINEC score and debridement. - Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/cellulitis-erysipelas-and-necrotising-fasciitis - Exam / course: NEET-PG · Subject: Medicine - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-14 - Last updated: 2026-10-14 - Reference basis: Harrison's Principles of Internal Medicine; Bailey and Love's Short Practice of Surgery - How to cite: "Cellulitis, Erysipelas and Necrotising Fasciitis", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/cellulitis-erysipelas-and-necrotising-fasciitis ## Direct answer Cellulitis is a spreading infection of the dermis and subcutaneous fat, most often caused by streptococci or Staphylococcus aureus. Erysipelas is its superficial, sharply demarcated form, typically from Streptococcus pyogenes, while necrotising fasciitis is a fast, deep infection that needs urgent surgical debridement. Recognising it early matters most, because pain out of proportion to the skin findings is the first clue. ## What you must remember - **Erysipelas:** a superficial infection with a raised, sharply demarcated border, classically on the face or legs and usually caused by Streptococcus pyogenes. - **Cellulitis:** a deeper infection with an ill-defined spreading edge, most often due to streptococci or Staphylococcus aureus. - **Pain out of proportion:** the earliest and most important sign of necrotising fasciitis, often before the skin looks dramatically abnormal. - **Type 1 and type 2:** type 1 necrotising fasciitis is polymicrobial with anaerobes, while type 2 is usually monomicrobial group A streptococcal infection and can cause toxic shock. - **LRINEC score:** six laboratory variables (CRP, white count, haemoglobin, sodium, creatinine and glucose) where a score of 8 or more signals high risk. - **Late signs:** crepitus, bullae and skin necrosis appear late, so surgery should not wait for them. - **Treatment:** urgent surgical debridement plus broad-spectrum intravenous antibiotics covering streptococci, staphylococci and anaerobes, with clindamycin added for toxin suppression in streptococcal disease. ## Telling the three apart at the bedside Most cases of skin infection need only the border, the pain and the systemic picture to sort them out. The sequence below moves from the simple bedside signs to the decisions that cannot wait. 1. **Look at the border:** a sharp, raised edge with a clear line of demarcation points to erysipelas, while a diffuse, poorly defined edge points to cellulitis. 2. **Assess the pain:** pain out of proportion to the skin findings, especially with rapid spread, fever and haemodynamic change, raises the alarm for necrotising fasciitis. 3. **Check the labs and the LRINEC score:** combine CRP, white count, haemoglobin, sodium, creatinine and glucose, where a score of 8 or more signals high risk. 4. **Image the deep plane:** CT or MRI can show fascial thickening, fluid and gas, but imaging should never delay surgical exploration in a suspicious patient. 5. **Operate early:** urgent debridement to viable tissue, repeated as needed, is the definitive treatment and is not replaced by antibiotics. 6. **Treat the organism:** broad-spectrum intravenous cover for streptococci, staphylococci and anaerobes, with clindamycin in streptococcal toxic disease, adjusted once cultures return. ## Where the exam tries to catch you Examiners test whether the student separates the superficial infections from the surgical emergency and does not wait for late signs. The traps below are the errors most often seen in this area. - **Trap:** erysipelas and cellulitis are the same disease under two names — **Correct:** erysipelas is a superficial form with sharp borders, usually from streptococci, while cellulitis is deeper with a poorly defined edge. - **Trap:** waiting for crepitus before operating — **Correct:** crepitus and bullae are late signs, so surgery is planned on pain out of proportion and rapid progression. - **Trap:** antibiotics alone treat necrotising fasciitis — **Correct:** dead tissue must be removed surgically, and antibiotics support debridement without replacing it. ## Frequently asked questions ### What is the difference between erysipelas and cellulitis? Erysipelas is a superficial infection with a raised, sharply demarcated border, usually caused by Streptococcus pyogenes. Cellulitis is a deeper infection with a poorly defined spreading edge, most often caused by streptococci or Staphylococcus aureus. ### What is the LRINEC score used for in necrotising fasciitis? The LRINEC score uses six routine laboratory values to estimate the risk of necrotising fasciitis in a patient with a soft tissue infection. A score of 8 or more indicates high risk, while a low score does not rule out necrotising fasciitis. ### Which organisms cause type 1 and type 2 necrotising fasciitis? Type 1 necrotising fasciitis is polymicrobial, usually involving anaerobes along with other bacteria, while type 2 is typically a monomicrobial infection with group A streptococci. Type 2 necrotising fasciitis is the form most associated with toxic shock syndrome. ### Why is surgical debridement needed in necrotising fasciitis? Surgical debridement removes necrotic fascia and subcutaneous tissue that antibiotics cannot reach effectively, so it is the definitive treatment for necrotising fasciitis. Debridement is repeated as needed, and antibiotics support the surgical control of the infection. ### What is the earliest clinical sign of necrotising fasciitis? Pain out of proportion to the skin findings is the earliest clinical sign of necrotising fasciitis, often with rapid spread, fever and systemic toxicity. Crepitus, bullae and skin necrosis are late findings, so surgery should not wait for them.