Necrotising Fasciitis
Last updated 19th November 2018 - Tom Heaton
Necrotising fasciitis is defined as a necrotising infection of the deep soft tissue layer.
The deep fascial layer can act as a potential space, allowing rapid spread of infection through this plane.
The relatively avascular nature of this area (and the necrotising effects of the infection) mean that immune system response on antibiotic delivery is poor.
The deep fascial layer can act as a potential space, allowing rapid spread of infection through this plane.
The relatively avascular nature of this area (and the necrotising effects of the infection) mean that immune system response on antibiotic delivery is poor.
Classification
The condition is usually classified as type 1-4 depending on the type of pathogen:
Type 1 is as a result of infection with a mixture of anaerobic and aerobic pathogens, usually in patients with some degree of immunosuppression e.g. DM, chronic alcohol use, chronic infection.
Pathogens include E. Coli, strep, staph,
Type 2 is caused by group A strep infection and can occur in anyone.
Type 3 is usually caused by marine water pathogen e.g. vibrio, and can occur after a relevant injury in these conditions.
Type 4 may occur in immunocompromised patients or following significant traumatic injury e.g. burns.
- Multimicrobial
- Group A streptococcus
- Gram negative monomicrobial
- Fungal
Type 1 is as a result of infection with a mixture of anaerobic and aerobic pathogens, usually in patients with some degree of immunosuppression e.g. DM, chronic alcohol use, chronic infection.
Pathogens include E. Coli, strep, staph,
Type 2 is caused by group A strep infection and can occur in anyone.
Type 3 is usually caused by marine water pathogen e.g. vibrio, and can occur after a relevant injury in these conditions.
Type 4 may occur in immunocompromised patients or following significant traumatic injury e.g. burns.
Risk Factors
Can be considered as:
- Immunosuppression
- Alcohol misuse
- DM
- IVDU
- Malignancy
- HIV
- CKD
- Chronic liver disease
- Alcohol misuse
- Trauma
- Traumatic wounds
- Bites
- Surgical wounds
- Traumatic wounds
Presentation
The diagnosis can be challenging to detect early on.
It may initially look like cellulitis.
Physical changes are often delayed.
The initial presentation will generally be of severe skin pain:
Key features of the early disease are:
Patients will often be significantly systemically unwell.
There can be notable skin changes that develop:
It may initially look like cellulitis.
Physical changes are often delayed.
The initial presentation will generally be of severe skin pain:
- Limbs (most common)
- Perineum (Fournier’s gangrene)
- Trunk
Key features of the early disease are:
- POOP - pain out of proportion of the skin changes
- POEM - pain outside erythematous margin (If there is one)
Patients will often be significantly systemically unwell.
There can be notable skin changes that develop:
- Erythema
- Bullae
- Oedema
- Skin discolouration (grey due to necrosis)
- Wooden hard feel
- Crepitus
- Anaesthesia may develop
Investigations
The key to diagnosis is exploratory surgery - this is needed in cases of high index of suspicion.
The macroscopic findings at surgery will include:
Additional investigations that may be helpful include.
The macroscopic findings at surgery will include:
- Grey necrotic tissue
- Lack of bleeding
- ‘Dishwater pus’
- Easy finger dissection
Additional investigations that may be helpful include.
- Bloods
- FBC - WBC usually elevated
- CRP - usually high
- CK - may be elevated
- FBC - WBC usually elevated
- Microbiology
- Blood cultures
- Blood cultures
- Imaging
- Xray - may show soft tissue gas (poor reliability/late)
- CT - soft tissue gas and fluid
- MRI
- Ultrasound
- Xray - may show soft tissue gas (poor reliability/late)
- Beside finger test
- Examination under local anaesthesia for worrying signs
- Examination under local anaesthesia for worrying signs
The Laboratory Risk Indicator for Necrotising Fasciitis (LRINEC) is one tool that has been used with the aim of helping differentiate necrotising fasciitis from other soft tissue infection.
It has limitations though (see link), and diagnosis at surgery remains the keystone.
https://www.mdcalc.com/lrinec-score-necrotizing-soft-tissue-infection
It has limitations though (see link), and diagnosis at surgery remains the keystone.
https://www.mdcalc.com/lrinec-score-necrotizing-soft-tissue-infection
Management
Aggressive debridement of affected tissue - cut back to margin of healthy (bleeding) tissue.
No infective tissue must be left.
Repeat explorations will often be needed.
Antibiotics have no real ability to affect the local condition (due to inability to penetrate to the site) but may help with systemic infection.
They should still be started early and have a broad spectrum (staph, strep, gram negative and anaerobes)
Supportive care may be needed in cases of a septic response or organ failure.
No infective tissue must be left.
Repeat explorations will often be needed.
Antibiotics have no real ability to affect the local condition (due to inability to penetrate to the site) but may help with systemic infection.
They should still be started early and have a broad spectrum (staph, strep, gram negative and anaerobes)
Supportive care may be needed in cases of a septic response or organ failure.
Epidemiology & Prognosis
This is an uncommon condition, with about 500 cases per year.
Mortality is high, even with early detection and intervention (20-40%)
Delayed diagnosis, additional pathology (e.g. comorbidity) and inadequate resection can increase mortality.
Mortality is high, even with early detection and intervention (20-40%)
Delayed diagnosis, additional pathology (e.g. comorbidity) and inadequate resection can increase mortality.
Links & References
- Welniak, TJ. Necrotising Fasciitis. EM in 5. 2015. https://www.youtube.com/watch?v=-VC1f88MZWU
- Tidy, C. Necrotising fasciitis. 2015. Patient.info. https://patient.info/doctor/necrotising-fasciitis-pro
- Nickson, C. Necrotising fasciitis. 2017. https://lifeinthefastlane.com/ccc/necrotising-fasciitis/
- MDCALC. LRINEC score. https://www.mdcalc.com/lrinec-score-necrotizing-soft-tissue-infection
