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Necrotizing Fasciitis

Necrotizing Fasciitis

Necrotizing fasciitis is a term that describes a disease condition of rapidly spreading infection, usually located in fascial planes of connective tissue that results in tissue necrosis (dead and damaged tissue). The disease occurs infrequently, but it can occur in almost any area of the body.

 

Although many cases have been caused by group A beta-hemolytic streptococci (Streptococcus pyogenes), most investigators now agree that many different bacterial genera and species, either alone or together (polymicrobial) can cause this disease. Occasionally, mycotic (fungal) species cause necrotizing fasciitis.

 

This condition was described by several people in the 1840s to 1870s, and Dr. B. Wilson in 1952 first termed the condition necrotizing fasciitis. It is likely that the disease has been occurring for many centuries before it was first described in the 1800s. Currently, there are many names that have been used loosely to mean the same disease as necrotizing fasciitis: flesh-eating bacterial infection or disease; suppurative fasciitis; dermal, Meleney, hospital, or Fournier's gangrene; and necrotizing cellulitis.

 

Body regions frequently have the term "necrotizing" placed before them to describe the initial localization of necrotizing fasciitis (for example, necrotizing colitis, necrotizing arteriolitis), but they all refer to the same disease process in the tissue.

 

Important in understanding necrotizing fasciitis is the fact that whatever the infecting organism(s), once it reaches and grows in connective tissue, the spread of the infection can be so fast (investigators suggest some organisms can progress about 3 centimeters per hour) that the infection becomes difficult to stop with both antimicrobial drugs and surgery.

 

Mortality (death) rates have been reported as high as 75% for necrotizing fasciitis associated with Fournier's (testicular) gangrene. Patients with necrotizing fasciitis have an ongoing medical emergency that often leads to death or disability if it is not promptly and effectively treated.

Symptoms

The symptoms and signs of necrotizing fasciitis vary with the extent and progression of the disease. Necrotizing fasciitis often affects the extremities or the genital area (Fournier gangrene), though any area of the body may be involved.

 

Early in the course of the disease, patients with necrotizing fasciitis may initially appear deceptively well, and they may not demonstrate any superficial visible signs of an underlying infection. Some individuals may initially complain of pain or soreness, similar to that of a "pulled muscle". However as the infection rapidly spreads, the symptoms and signs of severe illness become apparent.

 

Necrotizing fasciitis generally appears as an area of localized redness, warmth, swelling, and pain, often resembling a superficial skin infection (cellulitis). Many times, the pain and tenderness experienced by patients is out of proportion to the visible findings on the skin. Fever and chills may be present. Over the course of hours to days, the redness of the skin rapidly spreads and the skin may become dusky, purplish, or dark in color.

 

Overlying blisters, necrotic eschars (black scabs), hardening of the skin (induration), skin breakdown, and wound drainage may develop. Sometimes a fine crackling sensation may be felt under the skin (crepitus), signifying gas within the tissues.

 

The severe pain and tenderness experienced may later diminish because of subsequent nerve damage, leading to localized anesthesia of the affected area. If left untreated, continued spread of the infection and widespread bodily involvement invariably occurs, frequently leading to sepsis (spread of the infection to the bloodstream) and often death.

 

Other associated symptoms seen with necrotizing fasciitis may include malaise, nausea, vomiting, weakness, dizziness and confusion.

Causes

Necrotizing fasciitis is caused by bacteria in the vast majority of cases, though fungi can also rarely lead to this condition as well. Many cases of necrotizing fasciitis are caused by group A beta-hemolytic streptococci (Streptococcus pyogenes), either individually or along with other bacterial pathogens.

 

Group A streptococcus is the same bacteria responsible for "strep throat", impetigo (skin infection) and rheumatic fever. In recent years, there has been a surge in cases of necrotizing fasciitis caused by community-acquired methicillin-resistant Staphylococcus aureus (MRSA), often occurring in intravenous drug abusers.

 

Most cases of necrotizing fasciitis are polymicrobial and involve both aerobic and anaerobic bacteria. Additional bacterial organisms that may be isolated in cases of necrotizing fasciitis include Escherichia coli, Klebsiella, Pseudomonas, Proteus, Vibrio, Bacteroides, Peptostreptococcus and Clostridium among others.

 

In many cases of necrotizing fasciitis, there is a history of prior trauma, such as a cut, scrape, insect bite, burn, or needle puncture wound. These lesions may initially appear trivial or minor. Surgical incision sites and various surgical procedures may also serve as a source of infection. In many cases, however, there is no obvious source of infection or portal of entry to explain the cause (idiopathic).

 

After the bacterial pathogen gains entry, the infection can spread from the subcutaneous tissues to involve deeper facial planes. Progressive spread of the infection will ensue, and it can sometimes involve adjacent soft tissues as well, including muscle, fat, and skin.

 

Various bacterial enzymes and toxins lead to vascular occlusion, resulting in tissue hypoxia (decreased oxygen) and ultimately tissue necrosis. In many cases, these tissue conditions allow anaerobic bacteria to proliferate as well, allowing for the progressive spread of infection and continued destruction of tissue.

 

Individuals with underlying medical problems and a weakened immune system are also at increased risk of developing necrotizing fasciitis. Various medical conditions including diabetes, renal failure, liver disease, cancer, peripheral vascular disease, and HIV infection are often present in patients who develop necrotizing fasciitis, as are individuals undergoing chemotherapy and those taking corticosteroids for various reasons.

 

Alcoholics and intravenous-drug abusers are also at increased risk. Many cases of necrotizing fasciitis, however, also occur in otherwise healthy individuals with no predisposing factors.

 

For classification purposes, necrotizing fasciitis has been subdivided into three distinct groupings, primarily based on the microbiology of the underlying infection; type 1 NF is caused by multiple bacterial species (polymicrobial), type 2 NF is caused by a single bacterial species (monomicrobial) which is typically Streptococcus pyogenes, and type 3 NF (gas gangrene) is caused by Clostridiumspp.

 

Infection caused by Vibrio spp (frequently Vibrio vulnificus) is a variant form often occurring in individuals with liver disease, typically after ingesting seafood or exposing skin wounds to seawater contaminated by this organism.

Treatment

At the time of preliminary diagnosis, the patient needs to be hospitalized and started on intravenous antibiotics immediately. The initial choice of antibiotics can be made based upon the types of bacteria suspected of causing the infection, but many doctors believe that multiple antibiotics should be used at the same time to protect the patient from methicillin-resistant Staphylococcus aureus (MRSA), as well as infections with anaerobic bacteria, and polymicrobic infections.

 

Antibiotic susceptibility studies, done in the laboratory after the infecting organism(s) has been isolated from the patient, can help the physician choose the best antibiotics to treat the infected individual.

 

A surgeon needs to be consulted immediately if necrotizing fasciitis is suspected or preliminarily diagnosed. Debridement of necrotic tissue and collection of tissue samples, needed for culture to identify pathogens, are done by a surgeon.

 

The type of surgeon consulted may depend on the area of the body affected; for example, a urologic surgeon would be consulted for Fournier's gangrene. As is the case for immediate antimicrobial therapy, early surgical treatment of most cases of necrotizing fasciitis can reduce morbidity and mortality.

 

Many patients with necrotizing fasciitis are very sick and require admission to an intensive care unit. Sepsis and organ failure (renal, pulmonary, and cardiovascular systems) need to be treated aggressively to increase the patient's chance for recovery. Treatments such as insertion of a breathing tube, intravenous administration of fluids, and drugs to support the cardiovascular system may be required.

 

Although not available in many hospitals, hyperbaric oxygen therapy (oxygen given under pressure with the patient in a chamber) is sometimes used in treatment as the oxygen can inhibit or stop anaerobic bacterial growth and promote tissue recovery.

 

This therapy does not replace antibiotics or surgical treatment. However, hyperbaric oxygen therapy has been shown by researchers to further reduce morbidity and mortality by about 10%-20% in some patients when used in conjunction with antibiotics and surgery.

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