Necrotising soft tissue infection

Question 1

A 68 year old woman presents with evidence of spreading cellulitis of the anterior abdominal wall. What symptoms, signs and investigation results would support a diagnosis of necrotising acute soft tissue infection?

Answer 1

Impression
Impression is spreading cellulitis, concerned about the potential for a ecrotising soft tissue infections which is characterised by systemic features of infection, tissue destruction, and are associated with a high mortality rate. This is a surgical emergency so would progress quickly to definitive surgical treatment with debridement. Don’t delay surgery for investigations.

Two type of necrotising soft tissue infection
1: Polymicrobial (most common)
2: Mono microbial (Clostridium perfringens, Group A Streptococcal gangrene)
Physiological difference in necrotising vs other skin infection is small vessel necrosis, this gives rise to the pain out of proportion to clinical signs.

DDx

• simple skin infection
• cellulitis, erysipelas
• pyoderma gangrenosum (IBD associated)
• necrotising myositis

Goals

• thorough Hx/Ex/Ix
• treat emergently with surgical debridement and IV antibiotics

Question 2

Necrotising infection - History

Answer 2

History

• sx: systemic features of infection fevers, rigors, lethargy, local symptoms: pus, redness, pain (SOCRATES), crepitus
• Risks: recent wounds, previous NSTI, MRSA/strep colonisation, immunosuppression (diabetes, corticosteroids), obesity
• PMHx, meds, allergies
• Immunocompromised: diabetes, medications
• SNAP: alcohol, smoking which can impair wound healing

Question 3

Necrotising infection - Examination

Answer 3

Examination
- General appearance + vitals (generally very unwell?)
- Abdo/skin inspection: erythema, warmth, discolouration, suppuration, oedema
o cellulitis: poorly demarcated
o erysipelas: well demarcated
o NSTI: sub-cutaneous emphysema, dish-liquid discharge
- palpation: hard/wooden-like, induration
- swipe test: skin crepitus (gas formation), pain > than stimulus provided
- rapidly spreading
- if skin wound, then get ‘dishwater discharge’

Question 4

Necrotising infection - Investigation

Answer 4

Investigations
Is a clinical diagnosis, don’t wait for results for definitive surgical treatment; but can be supplemented with
- Soft tissue US or X-ray for gas production
- CT with contrast for tissue emphysema

• Bedside: Septic screen, wound swab and MCS
• Bloods: CRP/ESR, blood cultures, FBC, UEC, lactate, CK (necrotising myositis)
• Imaging: not indicated unless diagnostic uncertainty, altho CT would demonstrate gas in the soft-tissue planes

Question 5

Necrotising infection - Management

Answer 5

Management

• notify ID for consult, and gen surg for surgical management, may require ICU admission post-theatres.
• requires rapid management, literally spreads in minutes to hours.

Patients with NSTI require urgent surgical exploration and debridement of necrotic tissue as well as IV antibiotics and any necessary haemodynamic support (IV fluids, vasopressors, etc)

Supportive

• fluids, electrolytes
• antipyretics, antiemetics, analgesia
• vasopressors (guided by seniors/ICU)

Definitive

• Surgical exploration and debridement (can be medium for bacterial growth, debride down to healthy bleeding tissue) - debride down to bleeding tissue.
• IV antibiotics - empirical (meropenem, Pip-taz, +/- Vancomycin +/- clindamycin)
• hyperbaric oxygen post-operatively if available and appropriate

Question 6

Necrotising fasciitis - signs/symptoms

Answer 6

Symptoms

• pain out of proportion of presentation/wounds
• fevers +/- other systemic features of infection
• muscle pains
• open wound
• rapid progression

Signs

• subcut emphysema - crepitations
• extreme tenderness to palpation
• wooden-like skin; board-like
• may have no visible skin manifestations
• rapid progression
• dishwater discharge
• guarding and rigidity
• oedema