Ecthyma Gangrenosum

Synonyms: None

Etiology: Pseudomonas aeruginosa and other gram-negative bacteria, similar lesions caused by opportunistic fungi Associations: Immunosuppression, premature infants Clinical: Indurated plaques with black eschar and rim of erythema, favors axillae, inguinal folds, and perineum Histology: Mixed infiltrate of lymphocytes, neutrophils, plasma cells;

special stains of affected skin usually demonstrate the organism

Evaluation: Blood cultures, skin biopsy with fresh tissue culture, special stains on touch preps of skin biopsy, consider frozen section Treatment: Aimed at the specific infectious agent Prognosis: High mortality rate; worse with extensive skin disease, prolonged immunosuppression, and delayed treatment

Ecthyma gangrenosum describes a cutaneous infection with Pseudomonas aeruginosa that is manifested by necrotic plaques with an eschar. The infection usually occurs in immunosuppressed patients. Three to six percent of Pseudomonas septicemia is complicated by ecthyma gangrenosum (1). The term ecthyma gangrenosum was given by Hitschmann and Kreibich in 1897 in Germany to describe necrotic cutaneous plaques due to cutaneous involvement in disseminated Pseudomonas infection. However, ecthyma gangrenosum is now known to be a morphologic pattern of cutaneous infection caused by a wide variety of organisms.

Ecthyma gangrenosum usually starts as an erythematous macule, which subsequently forms a vesicle. Multiple lesions may occur. Lesions rapidly become indurated and may develop pustules or bullae, which slough and leave an ulcer. An eschar forms, with a rim of erythema (Figure 25.1). The disease has a strong predilection for axillae, inguinal folds, and perineum, so-called "apocrine" areas. Extremities, trunk, and face are affected less frequently. Though once regarded as cutaneous seeding during Pseudomonas bacteremia, most cases represent aggressive primary infection, which may disseminate in immuno-suppressed patients. Synchronous multiple lesions of the perineum, genitalia, and axillae are common. This pattern of infection supports the notion that ecthyma gangrenosum arises in the skin and then disseminates. In one series, folliculitis due to Pseudomonas aeruginosa O-11 from a hospital water supply rapidly developed into ecthyma gangrenosum in six hospitalized immunosuppressed patients (2). This represents a common scenario in which early lesions resemble a bacterial folliculitis, and then rapidly progress to typical ecthyma gangrenosum lesions. In the largest series of patients with ecthyma gangrenosum, over 75% were felt to originate in the skin, and two thirds primarily involved apocrine areas. Some patients developed septicemia (1).

The majority of patients who develop ecthyma gan-grenosum are neutropenic, either secondary to chemotherapy or due to primary immunodeficiency. The disease has also been described in HIV-infected patients in the absence of neutropenia (3). A neonatal form of the disease termed noma neonatorum occurs in premature infants. In addition to anogenital involvement, this presentation has a distinct orofacial predilection (4). A necrotizing stomatitis, the mucosal equivalent of ecthyma gangrenosum, has also been described in immunocompromised patients (5).

Classical ecthyma gangrenosum is usually caused by Pseudomonas aeruginosa, but may be caused by several other gram-negative bacteria (Table 25.1). Similar lesions in immunosuppressed patients may be caused by a multitude of opportunistic fungi. These patients usually do not present with the typical apocrine folliculocentric lesions. However, the morphologic features of individual lesions

Erythematous Papules With Eschar
Figure 25.1. Indurated erythematous plaque with central ulceration and eschar.

may closely resemble ecthyma gangrenosum. As in bacterial ecthyma gangrenosum, cutaneous lesions due to opportunistic fungi may be a manifestation of hematogenous dissemination with secondary seeding of the skin. Alternatively, they may represent primary invasive infection, which may then disseminate. Gastrointestinal and respiratory tracts and skin are common portals of entry for disseminated infections. Invasive infections of the skin may occur in previously normal skin, but are more likely to occur in areas that have had a disrupted barrier, such as sites of vascular access, venipuncture, burns, or surgical procedures.

The clinical presentation of ecthyma gangrenosum in an immunosuppressed patient constitutes a medical emergency. Investigation into the etiologic agent must be pursued urgently, so that appropriate antibiotic therapy can be instituted. A list of organisms known to cause ecthyma gangrenosum or similar lesions in the immuno-suppressed patient is given in Table 25.1.

The organisms listed in Table 25.1 cause ecthyma gangrenosum or lesions closely resembling it. However, numerous yeasts, and fungi causing hyalohyphomycosis and pheohyphomycosis, can cause invasive cutaneous infections in immunocompromised hosts. These cutaneous lesions may include subcutaneous and dermal nodules, or cellulitis. Since morphologic overlap with ecthyma gangrenosum could occur with a multitude of organisms, the list included in the table should not be viewed as comprehensive.

A clinical presentation of necrotizing papules and plaques in apocrine areas of an immunosuppressed patient strongly suggests ecthyma gangrenosum, but the differential diagnosis for a plaque or plaques with eschar is much wider, including true ecthyma caused by Staphylococcus or

Streptococcus species, arachnid or arthropod bite reactions, anthrax, tularemia, diphtheria, syphilitic chancre, herpes simplex virus infection, and orf. Similar lesions may develop in patients with septicemic plaque (Yersinia pestis) (20). Also in the differential diagnosis is Fournier's gangrene, a polymicrobial acute necrotizing infection of the genitalia. Causes include Streptococcus and Staphylo-coccus species, usually in combination with various gramnegative and anaerobic bacteria. This infection differs from ecthyma gangrenosum in its frequent occurrence in diabetics, severe pain, and tissue crepitus.

Cultures of the blood will reveal the organism in most cases of septicemic ecthyma gangrenosum. Since bacterial and fungal causes are morphologically indistinguishable, both bacterial and fungal cultures should be performed. The laboratory should be notified of the suspicion of opportunistic infection to minimize the possibility that a true positive culture will be dismissed as a contaminant. Tissue evaluation may include skin biopsy with touch preps, microbial stains, and culture. Touch preps may be stained with gram stain for bacteria and calcofluor white for fungi. Frozen sections from affected tissue with and without special stains may aid in more rapid diagnosis.

Biopsy findings in ecthyma gangrenosum include dermal edema and an infiltrate composed of neutrophils, lymphocytes, histiocytes, and plasma cells within the dermis and subcutaneous tissue (Figure 25.2A and 25.2B). There is vascular proliferation, and variable epidermal necrosis. Organisms may be found with special stains in most cases. The organisms are usually located within the interstitium and adventitia of venules. The findings in ecthyma gangrenosum differ from those of bacterial septic

Table 25.1. Causes of Ecthyma Gangrenosum and Similar Lesions in Immunosuppressed Patients

Bacteria

Pseudomonas aeruginosa Escherichia coli (6) Morganella morganii (7) Klebsiella pneumoniae (8) Citrobacter freundii (9) Xanthomonas maltophilia (10) Aeromonas hydrophilia (11)

Fungi

Curvularia sp. (12) Candida sp. (13) Fusarium sp. (14) Scytalidium dimidiatum (15) Metarrhizium anisopliae (16) Mucor sp. (17) Exserohilum sp. (18) Aspergillus niger (19)

Pseudomonas Vasculitis
Figure 25.2. (A) Deep ulcer with vascular congestion and neutrophil-rich infiltrate. (B) Numerous intravascular, perivascular, and interstitial Pseudomonas bacilli.

vasculitis in which there is vascular damage associated with fibrin thrombi and intraluminal bacteria (21).

Treatment of ecthyma gangrenosum is directed by the etiologic agent. However, initially, broad spectrum antibiotic therapy must be undertaken urgently because of the high mortality associated with delayed treatment. Prognosis in ecthyma gangrenosum is dependent upon the infectious agent, but also the degree and duration of immunosuppression and the extent of cutaneous involvement (21).

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