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NECROTIZING SKIN & SOFT TISSUE INFECTIONS
NECROTIZING CELLULITIS, NECROTIZING FASCIITIS, NECROTIZING MYOSITIS
OVERVIEW
Necrotizing soft tissue infections (NSTIs) include necrotizing forms of cellulitis, fasciitis, and myositis. These infections are characterized clinically by fulminant tissue destruction, systemic signs of toxicity, and high mortality. Accurate diagnosis and appropriate treatment must include early surgical intervention and antibiotic therapy.
Several different names have been used to describe the various forms of necrotizing infections; this is related in part to naming based on clinical features rather than surgical or pathologic findings. The degree of suspicion should be high since the clinical presentation is variable and prompt intervention is critical. The lay press has referred to organisms that cause NSTI as "flesh-eating bacteria."
CATEGORIES
NSTI can include involvement of the epidermis, dermis, subcutaneous tissue, fascia, and muscle Necrotizing infection may be categorized based on microbiology and presence or absence of gas in the tissues.
Distinguishing necrotizing fasciitis from necrotizing myositis may be difficult as skeletal muscle and fascia are involved in both syndromes. Necrotizing myositis primarily involves skeletal muscle, whereas necrotizing fasciitis primarily involves fascia.
Necrotizing cellulitis — Necrotizing cellulitis is typically caused by anaerobic pathogens and may be divided into two types: clostridial (usually caused by Clostridium perfringens; less frequently Clostridium septicum) and nonclostridial (caused by polymicrobial infection).
Necrotizing fasciitis — Necrotizing fasciitis is an infection of the deep soft tissues that results in progressive destruction of the muscle fascia and overlying subcutaneous fat. Infection typically spreads along the muscle fascia due to its relatively poor blood supply; muscle tissue is frequently spared because of its generous blood supply. Development of anesthesia may precede the appearance of skin necrosis and provide a clue to the presence of necrotizing fasciitis. Initially, the overlying tissue can appear unaffected; therefore, necrotizing fasciitis is difficult to diagnose without direct visualization of the fascia.
Necrotizing myositis — Necrotizing myositis is an infection of skeletal muscle typically caused by GAS (and other beta-hemolytic streptococci). It may be preceded by skin abrasions, blunt trauma, or heavy exercise. Necrotizing myositis is rare. One report noted 21 cases documented between 1900 and 1985; another review of over 20,000 autopsies noted 4 cases.
SYMPTOMS
Most skin infections do not result in the death of skin and nearby tissues. Sometimes, however, bacterial infection can cause small blood vessels in the infected area to clot. This clotting causes the tissue fed by these vessels to die from a lack of blood. Dead tissue is termed necrotic. Because the body's immune defenses that travel through the bloodstream (such as white blood cells and antibodies) can no longer reach this area, the infection spreads rapidly and may be difficult to control. Death can occur, even with appropriate treatment.
Some necrotizing skin infections spread deep in the skin along the surface of the connective tissue that covers muscle (fascia) and is termed necrotizing fasciitis. Other necrotizing skin infections spread in the outer layers of skin and are termed necrotizing cellulitis. Several different bacteria, such as
Streptococcus and Clostridia may cause necrotizing skin infections, but in many people, the infections are caused by a combination of bacteria. The necrotizing skin infection caused by streptococci has been termed “flesh-eating disease” by the lay press, but it differs little from the others.
Some necrotizing skin infections begin at puncture wounds or lacerations, particularly wounds contaminated with dirt and debris. Other infections begin in surgical incisions or even healthy skin. Sometimes people with diverticulitis, intestinal perforation, or tumors of the intestine develop necrotizing infections of the abdominal wall, genital area, or thighs. These infections occur when certain bacteria escape from the intestine and spread to the skin. The bacteria may initially create an abscess (a pocket of pus) in the abdominal cavity and spread directly outward to the skin, or they may spread through the bloodstream to the skin and other organs. People with diabetes are at particular risk of necrotizing skin infections.
The person usually feels very ill and has a high fever, a rapid heart rate, and mental deterioration ranging from confusion to unconsciousness. Blood pressure may fall because of toxins secreted by the bacteria and the body’s response to the infection (septic shock). People may develop toxic shock syndrome.
DIAGNOSIS
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A specialist's evaluation
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Laboratory tests
Our specialists make a diagnosis of necrotizing skin infection based on its appearance, particularly the presence of gas bubbles under the skin. X-rays may show gas under the skin as well.
A blood test usually shows that the number of white blood cells has increased (leukocytosis). The specific bacteria causing the infection are identified by laboratory analysis of blood or tissue samples. However, our specialists begin treatment before they have the laboratory test results.
PROGNOSIS
The overall death rate is about 30%. Older people, those who have other medical disorders, and those in whom the disease has reached an advanced stage have a poorer outcome. A delay in diagnosis and treatment and insufficient surgical removal of dead tissue worsens the prognosis.
TREATMENT
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Surgical removal of dead tissue
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Antibiotics
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Amputation if necessary
The treatment of necrotizing fasciitis is the surgical removal of the dead tissue plus antibiotics given by vein (intravenously). Large amounts of skin, tissue, and muscle must often be removed, and in some cases, an affected arm or leg may have to be removed (amputated).
People may need large volumes of intravenous fluids before and after surgery. Some doctors recommend treatment in a high-pressure (hyperbaric) oxygen chamber, but it is not clear how much this helps. People who also develop toxic shock syndrome may be given intravenous immune globulin.