Necrotizing fasciitis

Necrotising fasciitis (NF) is a group of lethal and rapidly progressive infections of the fascial and subcutaneous tissue (sometimes may involve muscles and skin) that are associated with necrotizing changes (1)

• it is relatively uncommon condition leading to significant morbidity and mortality

• although difficult to track demographically due to confusion arising from different eponyms used to express the same disease, it is estimated that around 500 new cases are diagnosed each year in the UK (1,3)

Diagnosis is clinical, and should be differentiated from cellulitis and other superficial infections of the skin. If caught late, there is secondary death of the overlying skin and often spread to deeper muscle. The treatment is rapid and comprehensive surgical debridement to stop the infective process (1,2).

• early clinical features include:
  • local erythema and swelling, myalgias, and pain - can mimic other soft tissue infections
    • often the initial focus of infection is a puncture wound, insect bite, scratch
    • usually begins like cellulitis with hot, red and tender skin, however, there may be an initial dissemination in the deeper tissue planes in the absence of surface changes
    • at the leading edge of infection, there is reddish or bronze discolouration of the skin and decreased sensation
    • the margin of infection advances rapidly along fascial planes
    • pain disproportionate to what would be expected in a superficial soft tissue infection is a surgical hallmark for consideration of necrotising fasciitis and requires prompt surgical referral and evaluation (3)
    • in many cases, common systemic signs, such as fever and tachycardia, are initially absent
    • in children may present with the same non-specific signs and symptoms to suffering from a viral illness (3)
  • timing of onset for the antecedent symptoms can be hours to seven days (mean two days)
    • however once the diagnosis is made, the evolution of signs can be rapid
      
      
• relatively late signs are classic findings of gas gangrene with crepitus and skin necrosis - septic shock has a poor prognosis by this stage
  • with thrombosis of perforating vessels, oedema, necrosis and sloughing of the skin occur
  • haemorrhagic bullae are relatively common
  • if this condition is untreated, toxaemia and death are the usual sequels

Risk factors for necrotising fasciiitis include factors such as diabetes mellitus and immunosuppression

Notes:

classification

Different terms are used to describe NF which are based on affected anatomy, microbial cause, and depth of infection e.g. -.

• classification by depth of infection - necrotizing fasciitis, myonecrosis, and necrotizing adipositis

• classification based on microbial cause - type I, type II. type III or type IV
  • type 1 (polymicrobial) is the most common,
  • type 2 (beta haemolytic Streptococcus pyogenes, monomicrobial),
  • type 3 (Clostridium species and Gram negative bacteria), and type 4 (fungal)
    
    
• classified according to anatomical sites - Fournier gangrene (involving the perineum) and Ludwig angina (involving submandibular and sublingual spaces)

Recent recommendations have suggested that the generic term 'necrotising soft tissue infections' should be used to describe all these conditions (2).

Reference:

• (1) Sultan HY, Boyle AA, Sheppard N.Necrotising fasciitis. BMJ. 2012;345:e4274.
• (2) Puvanendran R, Huey JC, Pasupathy S.Necrotizing fasciitis. Can Fam Physician. 2009;55(10):981-7
• (3) Diab J et al. Necrotising fasciitis. BMJ 2020;369:m1428.