What is Necrotizing fasciitis?
By Walter Little, Jr.
If Necrotizing fasciitis had a face, it would probably be the face of Aimee Copeland. Ms. Copeland suffered a laceration to her leg in a fall from a homemade zip line and, within a matter of days, was hospitalized fighting for her life. What is this so-called “flesh-eating” bacteria? According to the National Necrotizing Fasciitis Foundation (NNFF) website it is a “bacterial infection that attacks soft tissue and the fascia” and can result from either a minor trauma or other situation that allows bacteria to enter the body. This can include childbirth and invasive medical procedures such as surgery.
Necrotizing fasciitis is categorized as either Type I or Type II. Type I describes a polymicrobial infection (meaning several species of microbes are present) while Type II is used to describe a monomicrobial infection. Many types of bacteria can cause Necrotizing fasciitis (e.g., Group A streptococcus (Streptococcus pyogenes), Staphylococcus aureus, Vibrio vulnificus, and Aeromonas hydrophila). These infections are typically more likely to occur in persons with a compromised immune system[1].
Historically, Group A streptococcus has made up the majority of cases of Type II infections. However, as early as 2001, a more serious monomicrobial form of Necrotizing fasciitis has been observed with increasing frequency. The new strain is caused by methicillin-resistant Staphylococcus aureus (MRSA). Additionally, some published reports have implied a possible link between the use of non-steroidal anti-inflammatory drugs (NSAIDS) and NF. It should be noted, however, that the evidence of a link was weak due to a small number of case patients and whether the drugs just masked the symptoms of a secondary infection or were the cause per se.
What is the pathophysiology and symptoms of NF?
The term “flesh-eating bacteria” is actually a misnomer since the bacteria does not actually eat the flesh. Instead, it causes destruction of the skin and muscle by releasing toxins (virulence factors). These include: streptococcal pyogenic exotoxins. One of these, S. pyogenes, produces an exotoxin known as a “super antigen”. This so-called “super antigen” is capable of activating T-cells non-specifically resulting in the overproduction of cytokines and severe systemic illness (toxic shock).
Over seventy percent (70%) of cases of NF occurred in patients with one of the following clinical situations: suppressed immune system, diabetes, alcoholism / drug abuse, malignancies, and chronic systemic diseases[2], however, it also occasionally occurs in people with overall good general health.
The infection begins locally at the site of a trauma – in Amy Copeland’s case it was a laceration to her leg – which can either be severe, minor, or non-apparent. Persons with NF usually complain of intense pain that may seem excessive given the external appearance of the skin. As the disease progresses, often in a matter of hours, edema (swelling) of the affected tissue occurs. Patients also experience diarrhea and vomiting.
Patients with Necrotizing fasciitis typically have a fever and appear very ill. The mortality rate for NF has been reported as high as seventy-three percent (73%) if left untreated. Without medical care and surgical intervention the infection rapidly progresses and will eventually lead to death.
How is NF diagnosed?
LRINEC score
Use of the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score can be utilized to confirm persons presenting with signs of cellulitis to determine the risk Necrotizing fasciitis being present. It utilizes six (6) serologic measures: 1) C-reactive protein (CRP); 2) total white cell count (WBC); 3) hemoglobin; 4) sodium; 5) creatnine; and 6) glucose.
|
Test type
|
Serologic measure
|
Score
|
|
CRP (mg/L)
|
>150
|
Four (4) points
|
|
WBC (X 10^6 per mm3)
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<15
15-25
>25
|
Zero (0) points
One (1) point
Two (2) points
|
|
Hemoglobin (g/dL)
|
>13.5
11 – 13.5
<11
|
Zero (0) points
One (1) point
Two (2) points
|
|
Sodium (mmol/L)
|
<135
|
Two (2) points
|
|
Creatinine[3] (umol/L)
|
>141
|
Two (2) points
|
|
Glucose (mmol/L)
|
>10
|
One (1) point
|
How is NF treated?
Patients with NF are typically taken to surgery based on a high index of suspicion based on the patient’s signs and symptoms. With necrotizing fasciitis, aggressive surgical debridement (removal of infected and/or necrotic tissue) is necessary to prevent spreading and is the only treatment available. Diagnosis is confirmed by visual examination of affected tissue as well as by sending tissue samples for microscopic evaluation.
Since early treatment is often presumptive, antibiotics should be started as soon as NF is suspected. Initial treatment often includes a combination of intravenous antibiotics including penicillin, vanomycin, and cindamycin. Cultures are taken to determine the appropriate antibiotic coverage and modification – in the antibiotics – may be made once these results are obtained.
As in other injuries characterized by massive wounds or tissue destruction, hyperbaric oxygen treatment can prove to be a valuable adjunctive therapy, however, it is not widely available. Amputation of the affected limb(s) – or organ(s) – may be necessary as well as repeated exploratory surgery to remove additional necrotic tissue. The result is a large, open wound that requires a skin graft to heal properly. Due to the associated systemic inflammatory response, most patients require monitoring in an intensive care unit (ICU). Due to the extreme nature of these wounds – as well as the need for debriding and skin grafts – a burn center’s wound clinic may also be utilized for treatment of the patient.
[1] Kotrappa, K.S (1996, 2004) “Necrotizing fasciitis”, American Family Physician, Page 1691 - 1697
[2] Systemic disease is one that affects a number of organs and tissues, or affects the body as a whole.
[3] Creatine is a nitrogenous organic acid that occurs naturally in vertebrates and helps to supply energy to all cells in the body, primarily muscle.
