Ecthyma gangrenosum

Ecthyma gangrenosum is a type of skin lesion characterized by vesicles or blisters, which rapidly evolve into pustules and necrotic ulcers with undermined tender erythematous border. "Ecthyma" means a pus-forming infection of the skin with an ulcer, "gangrenosum" refers to the accompanying gangrene or necrosis. It is classically associated with Pseudomonas aeruginosa bacteremia, but it is not pathognomonic. Pseudomonas aeruginosa is a gram negative, aerobic bacillus.

This type of skin lesion was first described in association with Pseudomonas aeruginosa by L. Barker in 1897. It was given the name "ecthyma gangrenosum" by Hitschmann and Kreibich.

It mostly occurs in patients with underlying immunocompromise (e.g. malignancy or HIV). Although most cases are due to P. aeruginosa infection, recent reports of this skin lesion associate it with other microorganisms, such as Escherichia coli, Citrobacter freundii, Klebsiella pneumoniae, various other Pseudomonas species, and Morganella morganii.