Approach

Early recognition is important as disease progression is typically rapid. Necrotizing fasciitis is a life-threatening and time-critical surgical emergency.[2][4]​​​ Sepsis and multi-organ failure may be present.[2][34]​​​ Prompt referral to the surgical team and discussion with critical care is essential. Despite the need for laboratory testing including microbiologic testing and imaging when possible, necrotizing fasciitis remains primarily a clinical diagnosis with signs and symptoms that change rapidly over time.[2][4]​​

History

The speed of symptom progression should be determined. Inquire for specific risk factors such as:

  • Preceding skin lesions or breakdown

  • Trauma, surgery

    • Necrotizing fasciitis in the context of recent abdominal surgery or in the groin is most likely to be polymicrobial.

  • Immunosuppression due to chronic illness (e.g., diabetes mellitus, alcohol dependence)

  • Intravenous drug use

  • Chickenpox

  • Herpes zoster

It is important to remember that the inciting insult may be minor (e.g., an insect bite) or not recalled by the patient.[1][25]​ Exposure history may occasionally be helpful (e.g., freshwater exposure associated with Aeromonas hydrophila, saltwater exposure or consumption of raw oysters associated with Vibrio vulnificus); however, initial empiric antibiotic selection should be broad and not guided solely by historical exposures.​[9][15][25]

Other possible symptoms or signs of necrotizing fasciitis in a patient with cellulitis include lightheadedness, palpitations, nausea or vomiting, or delirium.

Physical exam

The diagnosis should be considered in a patient with cellulitis and clinical warning signs such as a positive quick Sepsis-Related Organ Failure Assessment (qSOFA; not specifically validated for necrotizing fasciitis). Altered mental status (Glasgow Coma Scale ≤15), systolic hypotension (systolic bp ≤100 mmHg), and elevated respiratory rate (≥ 22 bpm) suggest that a patient with cellulitis may have a necrotizing process requiring expedited surgical evaluation.[2]​ However, the patient may present with nonspecific or nonlocalized symptoms (e.g., acutely unwell with a normal temperature) or there may be severe signs with evidence of multi-organ dysfunction and shock.[2]

Anesthesia or severe pain over the site of cellulitis may be clues to an underlying subcutaneous infection.​​[1]​​​[16][19][20][35] The pain experienced with necrotizing fasciitis may be disproportionate to the visible skin changes. It should be noted that patients with necrotizing fasciitis can present with normal overlying skin, and that skin changes overlying group A streptococcal necrotizing fasciitis are a late sign.

Exam of the skin overlying the area of cellulitis may reveal crepitus, vesicles, bullae, grayish discoloration, or edema extending beyond erythema.[3]​ Subtle skin changes such as leakage of fluid and edema precede the overt skin changes of blistering and redness.

About half of cases occur in the extremities, with the remainder concentrated in the perineum, trunk, and head and neck areas.​​[1]​​​​​​[2][3][4][16][19][20]​ The most common site of group A streptococcal necrotizing fasciitis is the thigh and necrotizing fasciitis of a limb, especially the arm, is more likely to be due to group A streptococci than a polymicrobial infection. Some cases of necrotizing fasciitis may have associated myositis due to contiguous spread. This is more common in group A streptococcal than polymicrobial infections.

Necrotizing fasciitis in the context of recent abdominal surgery or in the groin is most likely to be polymicrobial.

Laboratory evaluation

All patients admitted with suspected necrotizing fasciitis should have a complete blood count with white cell differential, blood urea nitrogen (BUN), electrolytes, creatinine, and C-reactive protein (CRP) measured urgently. Some of these biomarkers are used for predictive scores including the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC). Raised lactate and procalcitonin may also be associated with increased likelihood of morbidity and mortality.[15]​ Arterial blood gases may be obtained if there is concern for respiratory compromise.  

Necrotizing fasciitis is frequently associated with a range of nonspecific laboratory abnormalities including:

  • Abnormally high or low white blood cell (WBC) count with or without a left shift (elevated percentage of polymorphonuclear leukocytes and/or bands). A low WBC count may be a sign of severe sepsis

  • Elevated BUN and creatinine due to intracellular volume depletion

  • Decreased serum sodium

  • Elevated CRP

  • Elevated serum creatine kinase

  • Elevated plasma lactate.

Blood cultures should be obtained before starting antibiotics, and may help identify the causative organism.[15]​ Gram stain and cultures from needle aspiration or deep tissue cultures obtained during surgical debridement or exploration may also yield a bacteriologic diagnosis.[5][15] Superficial skin swabs should be avoided.[15]

Molecular testing and next generation sequencing when available can help identify additional pathogens.[15]

Imaging

Imaging studies should not delay surgical intervention when diagnosis is clinically suspected.​​[2][3][5]​​[15]

In clinically stable patients, radiography may provide supportive evidence for a necrotizing process.

Plain radiography is frequently normal during the early stages; subcutaneous gas may be present as the disease progresses. The diagnosis should be strongly suspected if soft-tissue gas is visualized on radiologic examination, which may also demonstrate abnormalities in the involved soft tissue.​[1]​​​[2][16]​​[36]​​ However, soft-tissue gas is a late sign, and plain radiography has poor sensitivity for detecting signs of necrotizing infection.[15]

Ultrasound may help to differentiate simple cellulitis from necrotizing fasciitis and has the advantage that it can be rapidly performed at bedside.[2] In one prospective study, ultrasound findings of diffuse thickening of the subcutaneous tissue, accompanied by fluid accumulation greater than 4 mm in depth, had a sensitivity of 88% and specificity of 93%.[37]

Computed tomography (CT) and magnetic resonance imaging (MRI) offer higher sensitivity.[3][36] CT is indicated in abdominoperineal and cervicofacial infections to show the portal of entry of infection and to guide surgical intervention; for limb or peripheral necrotizing soft-tissue CT is of limited value.[15][36] MRI is more sensitive for assessing necrotizing soft-tissue infections of the limbs, and may show thickening of the fascia, deep fascial fluid or edema. However, these signs are not specific to necrotizing infection and may be seen in other soft-tissue infections such as cellulitis, and MRI may be difficult to organize in an emergency and is not recommended as the first-line imaging technique.[2]​​[3]​​[15]​​​[38]

In a meta-analysis, CT had sensitivity of 88.5% and specificity of 93.3%, while plain radiography had sensitivity of 48.9% and specificity of 94.0% for diagnosing necrotizing soft tissue infections.[39]

Early frozen-section soft-tissue biopsy can provide a definitive diagnosis and may be used if the diagnosis is unclear clinically or radiologically.[2] However, frozen-section soft-tissue biopsy requires specialist pathology expertise, takes time to perform, and is not widely available in all regions, including in the UK.[2]

Diagnostic criteria

The use of severity assessment scores may be helpful in identifying patients at high risk of systemic sepsis and, therefore, those who need urgent critical care and surgical assessment.[2]

Necrotizing fasciitis should be considered in a patient with cellulitis and clinical warning signs such as a positive quick Sepsis-Related Organ Failure Assessment (qSOFA; for use in settings other than the intensive care unit). However, no studies have specifically addressed the use of qSOFA, or the Sequential Organ Failure Assessment (SOFA; for use in the intensive care unit), in necrotizing fasciitis.

The LRINEC scoring system, based upon laboratory abnormalities (CRP, hemoglobin sodium, creatinine, glucose), has been developed in an attempt to assist with early discrimination of necrotizing fasciitis from less severe skin and soft tissue infections.[3][40]​​​​ In a 2019 meta-analysis, a LRINEC 6 was associated with a sensitivity of 68.2% (95% CI 51.4% to 81.3%) and specificity of 84.8% (95% CI 75.8% to 90.9%) for diagnosis of necrotizing soft tissue infections.[39]​ While validation studies have failed to demonstrate sufficient sensitivity or specificity to either diagnose or exclude necrotizing fasciitis, a higher LRINEC score on presentation has been associated with a higher risk of mortality in necrotizing fasciitis.​[39][41]​​​[42]

Consultation

Involving a range of experts with a multidisciplinary approach may improve management and prognosis, along with a high index of suspicion for the condition.[15]​ Senior decision makers should be involved early when necrotizing fasciitis is suspected, given that there is a low incidence and poor sensitivity of early clinical signs and in the absence of optimal noninvasive diagnostic tools.[15]​ An urgent surgical consultation for inspection, exploration, and debridement of infected tissue should be obtained as soon as the diagnosis is suspected.[3]​ Additional early consultations include involving an intensive care specialist.[15]​ Definitive bacteriologic diagnosis is best made from tissue specimens obtained from surgical debridement.[5]​ Staining of clinically affected tissue may provide an early indication of the causative organism(s). For example, small chains of gram-positive cocci suggest a streptococcal infection, whereas clumps of large cocci suggest Staphylococcus aureus. Culture growth of blood or tissue specimens identifies a bacterial cause. The infection may be monomicrobial or polymicrobial.​​[1][5][16]​​​​​[19][20][Figure caption and citation for the preceding image starts]: Late signs of necrotizing fasciitis with extensive cellulitis, induration, skin necrosis, and formation of hemorrhagic bullaeFrom: Hasham S, Matteucci P, Stanley PRW, et al. Necrotising fasciitis. BMJ. 2005 Apr 9;330(7495):830-3 [Citation ends].com.bmj.content.model.Caption@237e8b95[Figure caption and citation for the preceding image starts]: Split thickness skin grafting after surgical debridementFrom: Hasham S, Matteucci P, Stanley PRW, et al. Necrotising fasciitis. BMJ. 2005 Apr 9;330(7495):830-3 [Citation ends].com.bmj.content.model.Caption@52028f6c[Figure caption and citation for the preceding image starts]: Necrotizing fasciitis on the right abdomen of a 2-year old girl following varicella infectionFrom: de Benedictis FM, Osimani P. Necrotising fasciitis complicating varicella. BMJ Case Rep. 2009;2009:bcr2008141994 [Citation ends].com.bmj.content.model.Caption@432a47c5

[Figure caption and citation for the preceding image starts]: Small areas of skin necrosis in a young woman with cellulitis and necrotizing fasciitis of her lower abdomen 5 days after a cesarean sectionFrom: Hasham S, Matteucci P, Stanley PRW, et al. Necrotising fasciitis. BMJ. 2005 Apr 9;330(7495):830-3 [Citation ends].com.bmj.content.model.Caption@4185c4ca

Consultation with an infectious disease expert to assist with empiric antibiotic regimen, as well as subsequent appropriate de-escalation of therapy, is highly recommended.[15]

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