Necrotising Fasciitis

Question 1

Definition of Necrotising Fasciitis

Answer 1

Life threatening subcut. soft tissue infection that may extend to the deep fascia but not underlying tissue

Question 2

Epidemiology of Necrotising Fasciitis

Answer 2

Type I more common than Type II. Complicates 5% of invasive GAS infections

Question 3

Aetiology of Necrotising Fasciitis

Answer 3

Type I is polymicrobial infection - an anaerobe (bacteroides or peptosterptococcus) PLUS a favilitative anaerobe (E.coli, klebsiella, proteus) or non-GAS with or without staph aureus

Type II- monomicrobial infection caused by strep pyogenes(GAS), vibrio vulnificus, aermonas hydrophilia, panton-valentine leukocidin (PVL) positive staph auerus and MRSA

Mucormysis is a rare cause

Question 4

Risk factors for necrotising fasciitis

Answer 4

Strong: 
IVDU
Chickenpox/herpes zoster
Inpatient contact w GAS infection 
Non-traumatic skin lesions  (burns, psoriasis, cutaneous ulcers)

Weak:
Diabetes mellitus
Peripheral vascular disease
Immunocompromising conditions 
Chronic renal or hepatic insufficiency
Certain medications (corticosteroids, NSAIDs)

Question 5

Pathophysiology of Necrotizing fasciitis

Answer 5

Bacteria is introduced into skin and soft tissue from minor trauma, puncture wounds or surgery. Infection extends to fascia but not underlying muscle. Systemic illness includes fever, tachycardia and hypotension primarily due to action of bacterial toxins.

Founier’s gangrene: Type I necrotizing fasciitis of the scrotum or male perineum.

Question 6

Hx and Exam for necrotizing fasciitis

Answer 6

Presence of risk factors
Anesthesia or severe pain over site of cellulitis - pain experienced w necrotizing fasciitis may be disproportionate to visible skin changes
Fever
Palpitations, tachycardia, hypotension, tachypnoea, light headedness
Nausea and Vomiting

Uncommon:
Delirium 
Crepitus
Vesicles or Bullae
Grey discoloration of skin
Oedema or induration
Location of lesion

Question 7

Investigations for necrotising fasciitis

Answer 7

1. FBC + differential = abnormally high or low WBC
2. Serum electrolytes = hyponatremia
3. Serum urea + creatinine = elevated urea and creatinine levels
4. Serum CRP = elevated CRP levels
5. Creatinine Kinase = creatinine kinase levels may be elevated
6. Serum lactate = usually elevated lactate levels
7. Blood and tissue cultures = +ve may indicate polymicrobial or monomicrobial aetiology
8. Gram staining = indicates gram 0ve or gram +ve bacteria
9. ABG= hypoxemia, acidosis
10. Radiography = oedema extending along fascial plane and or soft tissue gas
11. Surgical exploration = necrotising soft tissue infection

Question 8

Management for necrotising fasciitis

Answer 8

If organism unknown:
surgical debridement + haemodynamic support + empiric broad spectrum abx
Vancomycin/Linezolid/Tedizolid/Daptomycin AND piperacillin+tazobactam / imipenem+alastatin / meropenem/ertrapenem AND clindamycin

Type I: polymicrobial
surgical debridement + haemodynamic support + empiric broad spectrum abx
Vancomycin/Linezolid/Tedizolid/Daptomycin AND piperacillin+tazobactam / imipenem+alastatin / meropenem/ertrapenem

Type II: due to GAS
surgical debridement + haemodynamic support + IV abx
1st line: benzylpenicillin sodium AND clindamycin
2nd line: vancomycin

Streptococcal toxic shock:
IV immunoglobulin

Type II due to staph aureus:
surgical debridement + haemodynamic support + IV abx
1st line MRSA: Vancomycin/Linezolid/Tedizolid phosphate /Daptomycin
2nd line MRSA: Ceftaroline/dalbavancin/telavancin
3rd line MSSA: nafcillin, oxacillin, cefazolin

Type II due to Vibrio vulnificus:
surgical debridement + haemodynamic support + IV abx
1st line: Doxycycline AND ceftrazidime/ceftriazone/ciprofloxacin

Type II due to aeromonas hydrophilia:
surgical debridement + haemodynamic support + IV abx
1st line: doxycycline AND ciprofloxacin
2nd line: doxycycline AND ceftriaxone or cefepime

Type II due to mucorales:
surgical debridement + haemodynamic support + antifungal therapy
1st line: amphotericin B lipid complex
2nd line: Isavuconazole

Persistent cosmetic + functional defects after debridement: reconstructive surgery