Ecthyma gangrenosum is a rare but serious cutaneous infection that is most commonly associated with Pseudomonas aeruginosa bacteremia. It usually occurs in patients who are critically ill and immunocompromised.
The lesions of ecthyma gangrenosum begin as painless, round erythematous macules and patches that develop into central pustules with surrounding erythema. A hemorrhagic vesicle appears at the center of the lesion and evolves into a gangrenous ulcer with a black eschar. Early lesions may progress to necrotic ulcers in as little as 12 hours. The lesions can be localized and solitary, or widespread.
Impaired humoral or cellular immunity leads to increased susceptibility to infections with Pseudomonas aeruginosa or other pathogens. In addition, breakdown of mechanical defensive barriers, such as the skin and mucosa, may allow infectious organisms to disseminate. The lesions of ecthyma gangrenosum result from perivascular bacterial invasion of arteries and veins in the dermis and subcutaneous tissues, producing a necrotizing vasculitis.
Ecthyma gangrenosum is typically and most commonly caused by Pseudomonas aeruginosa, but other bacteria, including Proteus species, Escherichia coli, and methicillin-resistant Staphylococcus epidermidis, have been implicated in similar lesions. A skin biopsy is taken for routine histology and special stains may also be done to rule out other organisms that may cause ecthyma gangrenosum-like lesions. Treatment of ecthyma gangrenosum involves prompt and aggressive antibiotic therapy, as well as supportive care.