Erysipelas — SCE Dermatology MCQ

Correct answer: B — Well-defined raised border with a sharp demarcation

The correct answer is B, well-defined raised border with a sharp demarcation. Erysipelas is a superficial infection confined to the upper dermis and superficial lymphatics, so the inflamed area has a palpable, raised edge with a clear step-off from normal skin, whereas cellulitis extends into the deeper dermis and subcutaneous fat and therefore spreads with an indistinct, flat, poorly demarcated margin. This border characteristic is the classic bedside sign used to separate the two entities clinically, since both conditions otherwise share erythema, warmth, swelling and tenderness. UK guidance on cellulitis and erysipelas notes that erysipelas typically has a sharper raised border compared with cellulitis, making this the single most reliable discriminator. Why the other options are wrong: D. Response to antibiotics: both conditions are treated with similar antibiotic regimens (usually flucloxacillin or penicillin) and both generally respond well, so treatment response does not distinguish them. C. Presence of fever: systemic upset with fever can occur in either erysipelas or cellulitis and is not specific enough to reliably differentiate the two. A. Involvement of the lower leg: the lower leg is the commonest site for both erysipelas and cellulitis in current practice, so site alone does not discriminate between them. E. Presence of lymphangitis: lymphatic streaking can occur with either superficial or deep skin and soft tissue infection and is not a specific or reliable distinguishing sign. Key point: A sharply demarcated, raised edge reflects erysipelas confined to the superficial dermis and lymphatics, while cellulitis has a poorly defined, non-raised margin from deeper tissue involvement.

Reference: NICE NG141, Cellulitis and erysipelas: antimicrobial prescribing (2019, updated), summarised via NICE-aligned UK clinical guidance; NICE CKS Cellulitis - acute, https://cks.nice.org.uk/topics/cellulitis-acute/