Necrotising Fasciitis

Question 1

Define Necrotising Fasciitis

Answer 1

Life-threatening subcutaneous soft-tissue infection that may extend to the deep fascia, but not to the underlying muscle

Question 2

What are the two main clinical forms of Necrotising Fasciitis and Fournier’s gangrene

Answer 2

Type I: polymicrobial infection with anaerobe e.g. bacteroides or Peptostreptococcus + facultative anaerobe e.g. enterobacterales or non-group A streptococcus

Type II: monomicrobial infection with streptococcus pyogenes (group A streptococci)

Fournier’s gangrene: Type I necrotising fasciitis of the scrotum or male perineum

Question 3

Aetiology of Necrotising Fasciitis

Answer 3

Type I: polymicrobial = anaerobe (bacteroides or peptostreptococcus) AND facultative anaerobe (E. coli, enterobacter, Klebsiella) or non-group A streptococcus ± S. aureus

Type II: Commonly Strep. Pyogenes

Bacteria are introduced into the skin and soft tissue from minor trauma, puncture wounds, or surgery. Infection extends through the fascia but not into the underlying muscle, and tracks along fascial planes extending beyond the area of overlying cellulitis

Question 4

Risk factors for Necrotising Fasciitis

Answer 4

Inpatient contact with index case (median interval 4 days person-person)
Varicella Zoster or herpes zoster (cutaneous port)
Cutaneous injury, surgery, trauma
Non-traumatic skin lesions e.g. eczema, psoriasis, cutaneous ulcers, burns
IVDU
Diabetes Mellitus
Peripheral vascular disease
Immunocompromising conditions e.g. HIV
Chronic renal or hepatic insufficiency
Medications e.g. corticosteroids, NSAIDs

Question 5

Symptoms of Necrotising Fasciitis

Answer 5

Anaesthesia or severe pain over site of cellulitis
Fever
Nausea and vomiting

Systemic signs of infection: palpitations, light-headedness

Can present with normal overlying skin and skin changes overlying group A streptococcal necrotising fasciitis are a late sign. Subtle skin changes such as leakage of fluid and oedema precede the overt skin changes of blistering and redness.

The most common site of group A streptococcal necrotising fasciitis is the thigh

Question 6

Signs of Necrotising Fasciitis

Answer 6

Systemic signs of infection: tachycardia, tachypnoea, hypotension

Delirium 
Crepitus
Vesicles or bullae
Grey discoloration of skin
Oedema or induration (Localized hardening of soft tissue of the body)

Question 7

Investigations for Necrotising Fasciitis

Answer 7

Surgical exploration as soon as suspected: necrotising soft-tissue infection

ABG: hypoxaemia, acidosis
FBC: abnormally high or low WBC ± left shift (polymorphonuclear leukocytes)
U+Es: hyponatraemia
Renal: U and Cr may be elevated
Serum CK: may be elevated
Serum lactate: Elevated
Blood and tissue cultures: Positive, may indicate polymicrobial or monomicrobial aetiology 
Gram stain: depends on the cause

Radiography, CT/MRI/USS: oedema extending along the fascial plane and/or soft tissue gas