What is ecthyma?

Ulcerative lesion extending to dermis (deep impetigo), punched out ulcer covered w/yellow crust surrounded by raised margins, heals slowly and scars (unlike impetigo), S.aureus/GAS/Pseudomonas (If IC) AKA ecthyma gangrenosum. It is necrotic covered with thick crust and surrounded by dark halo usually in lower limbs, could be induced by poor hygiene, IC, DM, alcoholism + Strep usually. heals slowly and leaves a scar