Overview
Necrotising fasciitis (NF) describes a bacterial infection of the skin and fascia, which can be categorised based on its aetiological causes:
- Type I NF – most common, often multiple mixed anaerobic species
- Type II NF – due to Streptococcus pyogenes
It can also be classed according to its presentation:
- Insidious – non-specific/variable symptoms, mild/absent localised pain at the affected site, insidious onset
- Acute (over days) – features develop over days, with pain out of proportion to clinical findings, can deteriorate over hours-days
- Fulminant –most severe type, extensive tissue necrosis over hours and sepsis
It is an emergency as it can spread rapidly and lead to soft tissue necrosis and death. It may be difficult to recognise in its early stages.
Fournier Gangrene
Fournier gangrene is a type of necrotising fasciitis affecting the perineum, characterised by scrotum pain and redness which can rapidly lead to gangrene. It is often secondary to perineal or urinary tract infections.
Epidemiology
- Around 500 people per year may have NF in the UK
Risk Factors
Risk factors include:
- Skin trauma – burns, injection, infections, trauma, skin infections (e.g. varicella zoster)
- Diabetes mellitus – especially if the patient is taking SGLT-2 inhibitors:
- Increased urinary glucose due to SGLT-2 inhibitors increases the risk of infection, which can lead to NF.
- Immunosuppression – such as HIV or immunosuppressant drugs
Presentation
Overview
Necrotising fasciitis usually affects the lower limb, particularly the perineum (known as Fournier gangrene), however, other parts can be affected. Features include:
- Erythema, heat, tenderness, and swelling at the affected site:
- The pain is usually severe and out of proportion to clinical findings
- There may be reduced sensation over the affected site (due to small vessel thrombosis and nerve damage)
- There may be oedema over the affected site
- Skin crepitus and gangrene may be seen in later stages
- Systemic upset – including fever and tachycardia
Necrotising fasciitis should always be suspected in anyone with a rapidly-progressing soft tissue infection with severe, disproportionate pain.
Management
Overview
If NF is suspected, the patient should be referred for urgent surgical debridement and broad-spectrum antibiotics, even before the investigation results.
It is a clinical diagnosis, however, blood cultures should be taken to identify the causative organism and its sensitivities.
