Necrotising fasciitis

Necrotising fasciitis is a medical emergency that is difficult to recognise in the early stages.

It can be classified according to the causative organism:

• type 1 is caused by mixed anaerobes and aerobes (often occurs post-surgery in diabetics). This is the most common type
• type 2 is caused by Streptococcus pyogenes

Risk factors

• skin factors: recent trauma, burns or soft tissue infections
• diabetes mellitus
  • the most common pre-existing medical condition
  • particularly if the patient is treated with SGLT-2 inhibitors
• intravenous drug use
• immunosuppression

The most commonly affected site is the perineum (Fournier's gangrene).

Features

• acute onset
• pain, swelling, erythema at the affected site
  • often presents as rapidly worsening cellulitis with pain out of keeping with physical features
  • extremely tender over infected tissue with hypoaesthesia to light touch
  • skin necrosis and crepitus/gas gangrene are late signs
• fever and tachycardia may be absent or occur late in the presentation

Management

• urgent surgical referral debridement
• intravenous antibiotics

Prognosis

• average mortality of 20%