Necrotising fasciitis (NF) is a medical emergency that affects the subcutaneous tissue and spreads across the facial planes but does not affect the underlying muscle.
- Severe pain that is disproportionate to the clinical findings.
- Anaesthesia over the site of infection
- Oedema and erythema - with the oedema extending beyond the erythema
Approximately 500 people in the UK present with NF annually (0.4 cases per 100,000), however, absolute data is lacking. Although incidence is low, mortality remains high.
🔢 Classification
There are 4 types of NF based upon the causative organism, but the main 2 are type 1 and type 2:
- Type 1 - polymicrobial infection caused by anaerobes. This is more common. For example Fournier’s gangrene.
- Type 2 - a monomicrobial infection usually caused by Group A streptococci (Streptococcus pyogenes), but may also be due to staph. aureus.
- Type 3 - caused by clostridial spp. (spores found in dirt for example, so gardeners, farmers, military are common cases) or vibrio spp. (from saltwater bodies of water).. It may be referred to as saltwater NF. It is rarer.
- Type 4 - fungal NF.
We can also classification according to clinical presentation based on clinical signs and speed of onset:
Fulminant
Most severe type with a poor prognosis. There will be extensive tissue necrosis, progressing over hours accompanied with sepsis.
Acute
Develops over days. Usually associated with an identifiable skin wound or trauma history. Pain is disproportionate with clinical findings.
Insidious
Insidious onset. There may be mild/absent pain at the site of the skin lesion.
⚠️ Risk factors
- Skin injury
- Immunosuppression
- Diabetes mellitus particularly, especially if the patient is on SGLT-2 inhibitors.
- IV drug use
- Varicella zoster infections
- Surgery
- Ulcerative conditions
😷 Presentation
Patients are typically septic. They look systemically unwell despite a localised wound.
- Anaesthesia/severe pain over infection site - the pain will be disproportionate to the visible skin changes.
- Erythema/cellulitis
- Oedema - this may be the only sign in early stages.
- Fever
- Tachycardia - may be absent or late presentation.
- Tachypnoea - may be absent or late presentation.
- Hypotension
- Grey skin - with overlying crepitus (crackling sensation as gas is pushed through the skin)
- Bullae - another late presentation.
🔍 Investigations
NF is diagnosed clinically.
Some investigations can be performed to help make a definitive diagnosis:
- ⭐️ CT will show subcutaneous emphysema due to gas produced.
- ⭐️ Surgical exploration - debridement is also needed.
- Necrotising soft-tissue infection will be present of course.
- Positive finger test
- Graim staining - of debrided tissue.
- Blood and tissue cultures
- FBC - may show raised WCC but can also be lowered if severely septic.
- U&Es - hyponatraemia, urea and creatinine raised
- CRP
- Creatine kinase - raised 2º to myonecrosis.
- Lactate
- G&S + clotting profile
A surgical method performed under LA. It involves making a 2cm incision to the deep fascia and using your finger to assess. Positive findings include:
- Lack of resistance to finger dissection
- Presence of greyish “dishwater” fluid
- Presence of necrotic tissue
- Absence of bleeding
💯 Scoring
The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) scoring system is used:
It looks at CRP, WBC, Hb, sodium, creatinine, and glucose. Any score <6 is considered low-risk.
🧰 Management
- A-E assessment
- Broad-spectrum IV antibiotics - such as:
- Piperacillin/tazobactam - for suspected NF. Started as soon as blood cultures are obtained.
- Vancomycin - for MRSA cover (type 2 NF).
- Clindamycin - for GAS cover (type 2 NF). It breaks down the streptococcal exotoxin.
- Benzylpenicillin - coupled with clindamycin for type 2 NF.
- Emergency surgical debridement needed along with empirical antibiotics. The debridement prevents spread to neighbouring tissue. The debrided tissue needs to be sent for cultures too.