Necrotizing Fasciitis (Flesh Eating Disease)

Original Editor - Sara Halliday & Ashley Walker from Bellarmine University's Pathophysiology of Complex Patient Problems project.

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Definition/Description

Necrotizing fasciitis is a bacterial infection that consists of rapidly progressing necrosis of fascia and subcutaneous fat that eventually results in necrosis of the overlying skin and muscle.  The most rapidly progressing type of necrotizing fasciitis is Group A, streptococcal infection, also known as flesh-eating bacteria. Necrotizing fasciits can also involve microbial infections with a singular bacteria (monomicrobial) or a combination of bacteria (polymicrobial).  Necrotizing fasciitis can occur due to several reasons (traumatic and non-traumatic) and in a variety of patient populations. Some conditions have been found to predispose patients to the risk of infection. Most of these conditions cause immunosuppression and include diabetes, malignancy, drug abuse, and chronic renal disease.

The progression of the infection begins with the introduction of bacteria to the site and typically a result of trauma to the skin, however, trauma is not a necessary component. Once the infection is seeded locally, the bacteria spreads through deep fascial planes causing widespread tissue damage and infection. The spread of bacteria can cause ischemia to the area due to thrombosis occurring in blood vessels which can eventually result in gangrene.

Epidemiology and etiology

Epidemiology

The number of cases reported for necrotizing fasciitis in adults is 0.40 cases per 100,000 people/year while the incidence in children is reportably higher at 0.08 cases per 100,000 people/year.  Necrotizing fasciitis is considered a rare condition, however, the mortality rate remains high. Evidence has estimated the mortality rate to be at 20-40%. According to the Center for Disease Control there is an estimated 9,000-11,500 cases of necrotizing fasciitis occur each year in the United States, with a resultant 1,000-1,800 deaths annually.

Etiology

Necrotizing fasciitis is caused by bacteria. The most common bacteria associated with necrotiing fasciitis after minor trauma is Group A streptococcus. When necrotizing fasciitis develops after surgery, it is likely a mix of bacteria. Upon entering the body, it rapidly reproduces and emits toxins/enzymes that damage fascia and soft tissue. The bacteria will shield itself from the body's immune system which speeds up the proliferation along tissue planes.

Any condition that disrupts the skin's characteristics can result in infection. Some of these conditions include skin trauma, infected needle (i.e. intravenous drug abusers), psoriasis, bed sores, chicken pox, and bug bites. Typically necrotizing fasciitis occurs following some type of trauma to the skin, however, non-traumatic causes have also been reported. The causative factor may be as trivial as a scratch or insect bite. There have also been reported cases of necrotizing fasciitis occurring following acupuncture treatment and joint aspirations. 

Early presentation

Characteristics/Clinical Presentation

The patient may initially present with increasing pain, tenderness to palpation to the local area and periwound, erythema, swelling, crepitus, purulent drainage and usually a history of some type of trauma. Complaints of flu-like symptoms (nausea, vomiting, fever, malaise etc.) are also common. Patients can present with symptoms of sepsis that include fever, tachycardia, altered mental state and diabetic ketoacidosis that typically accompanies trauma to the skin.

Clinical presentation of necrotizing fasciitis varies and can typically be mistaken for other pathologies, such as cellulitis and superficial skin infections. Awareness of the presentation of necrotizing fasciitis clinically is critical due to the rapid progression of the disease. Evidence has shown that accurate diagnosis is difficult with only 15% to 34% of patients with necrotizing fasciitis having the appropriate admittion diagnosis. Misdiagnosis often occurs due to the vague symptoms that may be present (i.e. erythema, fever, pain), or the lack thereof. 

Risk factors

• Diabetes (accosiated with 70.3% of patients in a 2003 study)
• Chronic disease
• Immunosuppresion
• Intravenous drug use
• Peripheral vascular disease
• Renal failure
• Underlying malignancy

Diagnostic procedures

• CT scans: Deep fascial thickening, enhancement, fluid and gas in the soft tissue planes in and around superficial fascia are indicators of necrotizing faciitis
• Ultrasound: Thickening and distortion of deep fascia, and fluid collections along deep fascia are denoted
• MRI: Deep fascial thickening, deep fascial fluid collections, and hyperintense T2W signal within muscles
  • Controversial topic as some authors state that fascial enhancement is an indicator, while other authors state that lack of fascial enhancement is a positive finding.  \

• Laboratory tests: (same as ones used for severe soft tissue infections)
  • Full blood count
  • Electrolytes
  • Erythrocyte sedimentation rate
  • C-reactive protein
    

A numerical score sheet, called the laboratory risk indicator for necrotizing fasciitis (LRINEC), was devised from lab parameters as a possible indicating tool for detection of necrotizing fasciitis. Score of ≥6 has a positive predictive value of 92% and a negative predictive value of 96%.

File:LRINEC.png

In addition, blood and pus cultures could be examined and surgical exploration may be indicated to confirm the diagnosis of necrotizing faciitis.

Differential diagnosis

• Cellulitis

Medical management

Medication

Necrotizing fasciitis is treated with antibiotics usually administered intravenously, however, until surgical debridement has occurred, tissue hypoxia limits the efficacy of intravenous antibiotics. A high dose antibiotic regimen is critical in the treatment of the infection in order to limit the amount of tissue damage that may occur. The inflammation that is associated with the infection causes intense pain and discomfort that is unrelieved by analgesic medications. These two clinical findings present in necrotizing fasciitis assist to differentiate it from cellulitis.

Surgery

• Debridement

Systemic Involvement

There are multiple systems that are compromised because of necrotizing fasciitis.  If untreated, NF can lead to multi-system organ failure.  Specific systems involved include:  integumentary, cardiovascular, pulmonary, gastrointestinal, genitourinary, and immunologic.  The integumentary system is involved because of the tissue decay spawned from the infection.  The cardiovascular system is implicated from the hypotension that occurs as a sign of NF.  In addition, heart failure can result from advancement of the condition.  The pulmonary system can be compromised from eventual respiratory failure that can occur in later stages.  Common signs of NF is nausea and vomiting, which affects the gastrointestinal system.  Renal failure can also develop which connects the genitourinary system involvement.  With fever being a common sign, the immunological system becomes affected as well.

Medical Management (current best evidence)

An aggressive form of treatment for Necrotizing Fasciitis is necessary due to the rapid progression of the infection once contracted. The typical management includes intravenous broad-spectrum antibiotics and early surgical debridement in order to remove the necrotic tissue.  Early recognition is vital for successful treatment. If detected during the early stages, surgical debridement can be minor and more localized to the infected epidermis, subcutaneous and adipose tissue. 

In the later stages of necrotizing fasciitis, systemic shock can occur resulting in failure of many organ systems. Respiratory failure, heart failure, low blood pressure and renal failure may occur in this stage. Limb amputation is necessary once the infection begins to spread to other organ systems.

Hyperbaric oxygen therapy has been proposed as an adjunct therapy for the treatment of necrotizing fasciitis. However, evidence has found conflicting results on the efficacy of this treatment.  In a recent systemic review, the main advantages of hyperbaric oxygen therapy in addition to standard regimes are tissue preservation and decreased mortality.  However, in another study, Golger et al found that the addition of hyperbairc oxygen therapy showed no improvement in mortality rate.  A need exists for higher levels of research to be conducted for more conclusive results.

                                                              Following initial Surgical Debridement

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Courtesy of University of Louisville Hospital

                                                                      After Surgical Debridement 

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Courtesy of University of Louisville Hospital

Physical Therapy Management (current best evidence)

Physical therapy management will primarily occur after surgical debridement.  The PT may utilize negative pressure wound therapy (NPWT) to enhance blood perfusion and promote granulation tissue, especially in the depth of the wound.  In addition, NPWT can remove exudate, which decreases the inhibitory mediators and matrix metalloproteinases that interfere with the healing process.  At times, pulse lavage with suction could be utilized for debridement.  In addition, non-contact, low frequency ultrasound can be used for debridement facilitation.  After the wound has healed, scar management is important in preventing adhesions.  Range of motion, mobility, and exercise is crucial in the prevention of contractures.

                                                                 Negative Pressure Wound Therapy

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Courtesy of University of Louisville Hospital

Differential Diagnosis

Certain conditions need to be considered during the diagnosis process for necrotizing fasciitis.  Those conditions include:

• Cellulitis
• Acute Epididymitis
• Gas Gangrene
• Hernias
• Orchitis
• Testicular Torsion
• Toxic Shock Syndrome

Resources

The National Necrotizing Fasciitis Foundation. Available online at http://www.nnff.org/

PubMed Health. Available online at www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002415/

References

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