Editing Necrotising fasciitis

''An infection of the deep soft tissues, that results in progressive destruction of the muscle fascia and overlying subcutaneous fat''

== '''Predisposing factors''' (20% of cases occur in patients with none of these factors) ==

** Older age
** Obesity
** Advanced diabetes
** Alcoholism
** Cirrhosis
** Chronic debilitation
** Vasculopathy
** IVDU
** Immunosuppression
** Malignancy
** Chemotherapy
** HTN
** COPD
** ESKD
** CCF
** Perianal abscess
** Perforated viscus
** Recent surgery


== '''Pathophysiology''' ==

** Rapidly progressive inflammatory infection of deep fascia
** Bacterial exotoxins such as haemolysin, streptolysis and leucocidin 
** Infection typically spreads along the muscle fascia due to its relatively poor blood supply, but muscle tissue itself is frequently spared
** There is associated thrombosis of dermal vessels leading to secondary necrosis of overlying subcutaneous tissues
** Skin ischaemia, anaesthesia and necrosis eventually appears, but the skin can appear normal even with quite severe underlying infection
** Results in liquefactive necrosis
** Sepsis from combination of exotoxins, toxic shock syndrome and massive cytokine response

**

**

== '''Classification''' ==

** Type I (polymicrobial - both aerobic and anaerobic bacteria - Fournier's)
*** Usually seen in elderly or those with underlying illness (diabetes, vascular disease, pressure ulcer, episiotomy, haemorrhoid/fissure)
*** Usually presents with gas in tissue
*** Typically seen with an anaerobic species (Bacteroides, Clostridium, or Peptostreptococcus) in combination with ''Enterobacteriacaeae'' (E coli, Enterobacter, Klebsiella, Proteus) and one or more facultative anaerobic streptococci (although not commonly group A strep)
*** The facultative anaerobes lower the local oxygen tension, allowing anaerobic proliferation
*** The anaerobes produce toxins and inhibit host phagocytosis
*** Marked leukaemoid reactions with Clostridial infection
** Type II (monomicrobial)
*** Usually Group A strep (GAS) or Staph aureus
*** Can occur in any age group and without underlying comorbidities
*** Half have a clear portal of entry and half do not (theorised to be haematogenous translocation from the throat to a site of blunt trauma or muscle strain)
*** 'M protein' is an important virulence determinant of GAS - M versions 1 and 3 are associated with streptococcal toxic shock syndrome, where pyrogenic exotoxins are produced, increasing cytokine production and contributing to shock
*** Usually seen with CRP >200, modestly increased WCC with marked left shift, and AKI in the absence of hypotension
** Type III (water-borne bacteria)
*** Vibrio, Aeromonas
*** Cirrhosis and eating contaminated oysters are risk factors
** Type IV (Candida and other fungi)


== '''Differential diagnosis''' ==

** Necrotizing cellulitis
*** Typically caused by anaerobes
*** Clostridial vs non-clostridial
**** Crepitus observed in both types
**** Sparing of fascia and muscles
*** Relatively mild systemically
** Cellulitis
*** Normal CK/AST
*** Not usually septic, apart from low-grade
** Pyoderma gangrenosum
*** IBD patients
*** No cellulitis
*** Violaceous ulcer edge
*** Less sepsis
*** Worsens with surgery
*** Normal fascial planes
*** Responds to steroids, does not respond to antibiotics
** Pyomyositis (abscesses) or necrotizing myositis (gangrene)
*** An infection of skeletal muscle typically caused by GAS and other beta-haemolytic streptococci
*** Preceded by skin abrasions, blunt trauma, or heavy exercise
*** Separate to clostridial myonecrosis
** DVT

== '''Diagnosis''' ==

** "'''Necrotising fasciitis is a surgical diagnosis characterised by friability of the superficial fascia, dishwater-grey exudate, and a notable absence of pus'''."
** Classically:
*** Oedema (75%)
*** Erythema (72%)
*** Severe pain (72%)
*** Tenderness (68%)
*** Fever (60%)
*** Skin bullae or necrosis (38%)
** Differentiating from cellulitis:
*** Recent surgery
*** Pain out of proportion to clinical signs
*** Hypotension
*** Skin necrosis
*** Haemorrhagic bullae
*** Elevated CK and AST suggest injury to deeper tissue
** '''Scoring systems'''
*** '''LRINEC'''
**** LRINEC: high specificity for severe disease, but PPV is 57-92% with a score of 5.8 or higher
****
** '''Bedside exploration'''
*** LA
*** Area of greatest oedema/necrosis
*** Thin dishwasher-fluid like exudate, not frank pus
*** Non-contractile muscles
*** Send for urgent MCS and histo


== '''Clinical approach''' ==

** '''Indications for immediate exploration in theatre:'''
*** Crepitus or gas in tissue on imaging
*** Skin discolouration or necrosis
*** Thin, foul-smelling wound discharge
*** Rapid progression clinically
*** Severe pain out of proportion to skin findings
** '''Suspicious for NF with systemic signs, but not convincing:''' bedside cut-down, then LRINEC score, imaging and observation/medical management
** '''Possible diagnosis, but systemically well:''' LRINEC score, imaging and observation/medical management


== '''Resuscitation''' ==

** Blood cultures first
** Bacterial haemolysis often occurs, meaning haematocrit drops before Hb. Base transfusion on haematocrit rather than Hb.
** Need to give a lot of IVF, and albumin along with it
** Antibiotics: 
*** First-line: meropenem 1g TDS/tazocin 4.5g TDS + vancomycin 25-30mg/kg loading dose + clindamycin 600mg TDS/lincomycin 600mg TDS
*** Add ciprofloxacin 400mg TDS if there is a risk of water-borne infection
*** Severe penicillin allergy: generally still give meropenem, but 1% risk of cross-reactivity, seek ID advice. They may advise a regime of gentamicin or ciprofloxacin and metronidazole instead. 
** IVIg has been shown to reduce 30-day mortality from 33% to 15% in a 2018 meta-analysis, but only in the setting of setreptococcal infection
** Droplet and contact precautions for first 24 hours, if suspicious for GAS

== '''Surgery''' ==

** Peri-op factors
*** Faecal diversion?
*** Amputation?
*** Second-look within 48 hours
*** Early consideration of reconstruction - SSG?
*** Remember to ensure they have cross match/G+H
*** Should have second pair of eyes
** Operative debridement
*** Prep and drape widely
*** Debride widely - be brutal - need clear margins
*** Fat that glistens, muscle that twitches, skin that bleeds
*** Send tissue for Gram stain, culture and histopathology

== '''Post-op''' ==

** Hyperbaric oxygen treatment MIGHT be useful but jury definitely still out
** If the Gram stain returns as Gram-positive rods, be concerned for Clostridial myonecrosis (gas gangrene) and have a lower threshold for subsequent amputation

== '''Outcome''' ==

** Mortality
*** Polymicrobial infection 21%
**** Fournier's 22-40%
**** Cervical necrotizing fasciitis 22%
**** Neonatal NF - 59%
*** Monomicrobial NF 14-34%
** Worse prognostic factors:
*** WCC >30
*** Serum creatinine >177
*** Age >60
*** Streptococcal TSS
*** Clostridial infection
*** Delay in surgery >24 hours
*** Infections involving the head, neck, thorax, or abdomen

[[Category:Skin, soft tissue and wounds]]
[[Category:Intern education]]