Necrotising fasciitis

Question 1

Define

Answer 1

Subcutaneous soft-tissue infection which may extend to the deep fascia but NOT underlying muscle

Question 2

Causes

Answer 2

T1 (more common) – polymicrobial infection of subcutaneous tissue (anaerobe e.g. Bacteriodes or Peptostrep + facultative anaerobe e.g E.coli, enterobactoer, klebseiella)

T2 – monomicrobial infection of subcut tissue (strep pyogenes (GAS), staph A, MRSA, Aeronmonas hydrophilia and vibrio vuknificus)

Question 3

Risk factors:

Answer 3

• Cutaneous injury, surgery or trauma
• DM
• PVD
• Immunocompromised
• Chronic renal/ hep insufficiency
• Chickenpox
• Herpes zoster
• IV drug use
• Certain meds (e.g. corticosteroids)

Pathophysiology:

Bacteria are introduced into the skin and soft tissue from minor trauma, puncture wounds, or surgery. However, in up to 20% of cases no primary site of infection is identified. Infection extends through the fascia but not into the underlying muscle

Question 4

Epidemiology

Answer 4

T1 is more common than T2

Question 5

Symptoms and signs

Answer 5

Anesthesia or severe pain over site of cellulitis

Signs and symptoms of systemic infections: fever, palpitations, tachycardia, tachypnoea, hypotension and lightheadedness, N+V, delirium

Discoloration of skin

Question 6

Investigations

Answer 6

FBC – high WBC (if v. low may be a sign of sepsis)

U&Es – hyponatremia, high urea and cr, high crp

high CK, lactate (systemic infection finding)

+ve blood and tissue cultures – definitive diagnosis

Xray/CT/MRI in all pts with necrotising fascitis if clinically app – may show abnormalities of soft tissue

Surgical inspection, exploration, and drainage of infected tissue