A 42-year-old woman presents with a sharply demarcated, raised, bright red plaque over the left cheek with a palpable advancing border and marked tenderness. She has a low-grade fever of 38.2 degrees C. The lesion spares the deeper subcutaneous tissue. Which organism is the most likely cause?

• A Streptococcus pyogenes ✓
• B Staphylococcus aureus
• C Pseudomonas aeruginosa
• D Haemophilus influenzae

Explanation

Erysipelas is a superficial dermal infection involving the upper dermis and superficial lymphatics, producing a sharply demarcated, raised, tender plaque, classically on the face or lower leg. It is caused almost exclusively by Streptococcus pyogenes. Staphylococcus aureus causes cellulitis and carbuncles, which are less demarcated and involve deeper tissue. Pseudomonas causes ecthyma gangrenosum in neutropenic patients.

Reference: Rook's Textbook of Dermatology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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