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" means the gangrene or necrosis. It is the pathognomonic of Pseudomonas aeruginosa bacteremia. Pseudomonas aeruginosa is a gram negative, aerobic, coccobacillus bacterium.
It mostly occurs in patients with underlying immunocompromised conditions (e.g. malignancy). Although most cases are found in Pseudomonas aeruginosa infection, there are recent reports of this skin lesion associated with other microorganisms, such as Escherichia coli, Citrobacter freundii, Klebsiella pneumonia, various other Pseudomonas species, and Morganella morganii.
The primary skin lesion usually starts with a macule that is painless, round and erythematous. Then, it develops into a pustule, and then a bulla with central hemorrhagic focus. The bullae progresses into an ulcer which extends laterally. Finally it becomes a gangrenous ulcer with central black eschar surrounded by erythematous halo.
The organism enters directly through the breakdown of mechanical defense barriers such as mucosa or skin. Immunocompromised conditions make the patient more susceptible to this infection and septicemia. In case of septicemia, the bacteria reaches the skin via the bloodstream. Defective humoral or cellular immune system increases the risk because the organism is not able to be cleared from the bloodstream. The main mechanism of the organism that is causing the typical skin lesions is the invasion of the organism into the arteries and veins in the dermis and subcutaneous tissues of the skin. This perivascular invasion leads to nodular formation, ulceration, vasculitis and necrosis due to impaired blood supply. Perivascular involvement is achieved by direct entry of bacteria through the skin or hematogenous spreading in case of sepsis.
Diagnosis is made by clinical observation and the following tests.
(1) Gram stain of the fluid from pustules or bullae, and tissue swab.
(2) Blood culture
(3) Urine culture
(4) Skin biopsy
(5) Tissue culture
The main organism associated with ecthyma gangrenosum is Pseudomonas aeruginosa. However, multi-bacterial cases are reported as well. Prevention measures include practicing proper hygiene, educating the immunocompromised patients for awareness to avoid possible conditions and seek timely medical treatment.
Treatments and prognosis
Treatments involve antibiotics that cover for Pseudomonas aeruginosa. Antipseudomonal penicillins, aminoglycosides, fluoroquinolones, third generation cephalosporins or aztreonam can be given. Usually, the antibiotics are changed according to the culture and sensitivity result. In patients with very low white blood cell counts, Granulocyte-macrophage colony-stimulating factor may be given. Depending on the causal agents, antivirals or antifungals can be added.
Surgery will be needed if there is extensive necrosis not responding to medical treatments.
A recent retrospective study of all cases of Ecthyma gangrenosum from 2004-2010 in a university hospital in Mexico shows that neutropenia in immunocompromised patients is the most common risk factor for ecthyma gangrenosum.
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