Ecthyma gangrenosum (EG) is a cutaneous manifestation of gram-negative bacteremia, most commonly secondary to Pseudomonas aeruginosa. It is seen predominantly in immunocompromised patients due to immunodeficiency syndromes or immunosuppressive therapy, or in chronic disease states such as chronic lung disease, chronic neurological disease, severe burns, malnutrition, and diabetes mellitus. However, characteristic clinical lesions can also develop in immunocompetent individuals without associated sepsis.

Characteristic purpura or eschars develop when proliferating microorganisms invade the adventitia and media of blood vessels, causing occlusion and ischemic necrosis. Bacterial organisms include P aeruginosa, other species of Pseudomonas, Escherichia coli, Klebsiella pneumoniae, Vibrio vulnificus, Serratia marcescens, Aeromonas hydrophila, Citrobacter freundii, Stenotrophomonas maltophilia, Morganella morganii, and Moraxella species.

Severe complications such as osteomyelitis may occur from infection with P aeruginosa. The course depends on the underlying disease, but once manifestations of shock appear, the patient may quickly and irreversibly decline. Disseminated intravascular coagulation (DIC) may appear with gram-negative sepsis. Most patients are systemically ill and have associated fever, chills, and hypotension. Diabetic patients, however, may have few symptoms early in the disease. EG is seen in approximately 1%-13% of patients with P aeruginosa sepsis. The mortality rate ranges from 18%-96%.