(Table 1) Necrotizing fasciitis, formerly called streptococcal gangrene, may be associated with group A Streptococcus or mixed aerobic anaerobic bacteria or may occur as a component of gas gangrene caused by Clostridium perfringens. Strains of MRSA that produce the Panton-Valentine leukocidin (PVL) toxin have been reported to cause necrotizing fasciitis. Early diagnosis may be difficult when pain or unexplained fever is the only presenting manifestation. Swelling then develops and is followed by brawny edema and tenderness. With progression, dark-red induration of the epidermis appears, along with bullae filled with blue or purple fluid. Later the skin becomes friable and takes on a bluish, maroon, or black color. By this stage, thrombosis of blood vessels in the dermal papillae (Fig. 1) is extensive. Extension of infection to the level of the deep fascia causes this tissue to take on a brownish-gray appearance. Rapid spread occurs along fascial planes, through venous channels and lymphatics. Patients in the later stages are toxic and frequently manifest shock and multiorgan failure.

Table1. Skin and Soft Tissue Infections

Fig1. Structural components of the skin and soft tissues, superficial infections, and infections of the deeper structures. The rich capillary network beneath the dermal papillae plays a key role in the localization of infection and in the development of the acute inflammatory reaction..

Necrotizing fasciitis caused by mixed aerobic–anaerobic bacteria begins with a breach in the integrity of a mucous membrane barrier, such as the mucosa of the gastrointestinal or genitourinary tract. The portal can be a malignancy, a diverticulum, a hemorrhoid, an anal fissure, or a urethral tear. Other predisposing factors include peripheral vascular disease, diabetes mellitus, surgery, and penetrating injury to the abdomen. Leakage into the perineal area results in a syndrome called Fournier gangrene, characterized by massive swelling of the scrotum and penis with extension into the perineum or the abdominal wall and the legs.

Necrotizing fasciitis caused by S. pyogenes has increased in frequency and severity since 1985. There are two distinct clinical presentations: patients without, versus those with, a defined portal of bacterial entry. Infections in the first category often begin deep at the site of a nonpenetrating, relatively minor trauma, such as a bruise or a muscle strain. Seeding of the site via transient bacteremia is likely, although most patients deny antecedent streptococcal infection. Affected patients present with only severe pain and fever and are frequently misdiagnosed (e.g., thrombophlebitis), given pain-relieving drugs, and sent home. Later in the course, the classic signs of necrotizing fasciitis, such as purple (violaceous) bullae, skin sloughing, and progressive toxicity, develop. Mortality in this setting is high, and survivors often undergo repeated surgeries including amputations. In infections of the second type, S. pyogenes may reach the deep fascia from a site of cutaneous infection or penetrating trauma. These patients have early signs of superficial skin infection with progression to necrotizing fasciitis. In either setting, toxicity is severe, and renal impairment may precede the development of shock. In 20–40% of cases, myositis occurs concomitantly, and, as in gas gangrene, serum creatine phosphokinase levels may be markedly elevated. Necrotizing fasciitis due to mixed aerobic–anaerobic bacteria may be associated with gas in deep tissue, but gas usually is not present when the cause is S. pyogenes or MRSA. Prompt surgical exploration down to the deep fascia and muscle is essential. Necrotic tissue must be surgically removed, and Gram staining and culture of excised tissue are useful in establishing whether group A streptococci, mixed aerobic–anaerobic bacteria, MRSA, or Clostridium species are present.

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مواضيع ذات صلة

Myositis and Myonecrosis

Cellulitis

Laboratory Diagnosis of Francisella

Laboratory Diagnosis of Bordetella pertussis, Bordetella parapertussis, and Related Species

Epidemiology and Pathogenesis of Bordetella pertussis, Bordetella parapertussis, and Related Species

Group B Streptococcal Disease

Streptococcal Toxic Shock Syndrome

Signs and Symptoms of Streptococcal Infections

Corynebacterium diphtheriae

Clostridium tetani

Laboratory Diagnosis of Brucella

Epidemiology and Pathogenesis of Helicobacter