Necrotizing Soft Tissue Infections (NSTI)
1. DEFINITION & OVERVIEW
NSTIs คือการติดเชื้อของ soft tissue ที่มีลักษณะ rapidly progressive tissue necrosis, systemic
toxicity และ mortality สูง
ครอบคลุม
- Necrotizing
fasciitis
- Necrotizing
myositis
- Necrotizing
cellulitis
👉 Key principle: Early
recognition + early surgical debridement = survival
2. CLASSIFICATION (by microbiology)
Type I – Polymicrobial
- Aerobes
+ anaerobes
- Common
organisms
- Enterobacteriaceae
(E. coli, Klebsiella, Enterobacter)
- Anaerobes
(Bacteroides, Clostridium, Peptostreptococcus)
- Common
settings
- Diabetes,
PVD, elderly
- Fournier
gangrene
- Head
& neck NSTI (odontogenic source)
Type II – Monomicrobial
- Most
commonly Group A Streptococcus (GAS)
- Sometimes
Staphylococcus aureus
- Can
occur in previously healthy patients
- Often
associated with streptococcal toxic shock syndrome (STSS)
Special pathogens
- Vibrio
vulnificus →
seawater exposure, cirrhosis, raw oyster
- Aeromonas
hydrophila →
freshwater trauma
3. RISK FACTORS
NSTI can occur with or without comorbidities
Common risk factors:
- Diabetes
mellitus (most important)
- Minor
trauma / muscle strain
- Skin
breach (insect bite, injection drug use)
- Recent
surgery (GI, GU, GYN)
- Immunosuppression,
malignancy, obesity
- Cirrhosis,
alcoholism
- Pregnancy
/ postpartum
- SGLT2
inhibitors →
Fournier gangrene
- NSAIDs
(may mask symptoms)
4. CLINICAL MANIFESTATIONS (Red flags 🚩)
Key features
- Pain
out of proportion
- Rapid
progression (hours–days)
- Systemic
toxicity ± shock
Common findings:
- Erythema
(poorly demarcated)
- Edema
beyond erythema
- Severe
pain → later hypoesthesia/anesthesia
- Fever,
tachycardia
- Crepitus
- Bullae,
skin necrosis, ecchymosis
Classic clue
Early severe pain →
later loss of sensation
5. COMMON SITES
- Lower
extremities (most common)
- Perineum
(Fournier gangrene)
- Head
& neck (odontogenic →
mediastinitis risk)
- Neonates
(perineum, abdominal wall)
6. LABORATORY FINDINGS
- Nonspecific
- Leukocytosis,
hyponatremia
- Elevated
CRP, lactate
- ↑ CK / AST → suggests deep
muscle/fascial involvement
⚠️ LRINEC
score
- Variable
sensitivity
- ❌
Do NOT use to rule out NSTI
Blood cultures:
- Positive
~60% in type II NSTI
- Lower
yield in polymicrobial infections
7. DIAGNOSIS – KEY POINT
Diagnosis is made by SURGICAL EXPLORATION
When to suspect NSTI
- Severe
pain + systemic illness
- Rapid
progression
- Crepitus
or skin necrosis
Imaging
- CT
scan: best initial imaging (+ IV contrast ถ้าสงสัยปานกลาง)
- Gas
in soft tissue = highly specific
- MRI:
overly sensitive, may overestimate disease
- Imaging
must NOT delay surgery
8. MANAGEMENT (Emergency)
8.1 Surgical Management
- Immediate
aggressive debridement
- Repeat
exploration every 24–48 hrs
- Amputation
if necessary for source control
⏱️ Surgery < 24 hrs (ideally
< 6 hrs) → better
survival
8.2 Empiric Antibiotic Therapy
Start immediately after blood cultures
Recommended empiric regimen
- Carbapenem
(Meropenem 1 g (20 MK) q 8 h) or Piperacillin–tazobactam 4.5 g (75 MK) q 8 h
- +
MRSA coverage (vancomycin 15 MK q 8 h or daptomycin)
- +
Clindamycin 600-900 mg q 8 h (40 MKD) (antitoxin effect)
📌 Clindamycin is critical
for toxin suppression (GAS, S. aureus)
Tailor therapy once cultures available
8.3 Targeted Therapy
- GAS
NSTI → Penicillin
+ Clindamycin
- Clostridial
infection →
Penicillin + Clindamycin
- Polymicrobial
→ Vancomycin +
carbapenem / BL-BLI
- Water
exposure → cover
Aeromonas / Vibrio
Duration:
- Until
no further debridement needed
- Hemodynamic
stability
- Often
≥
2 weeks
9. ADJUNCTIVE THERAPY
Hemodynamic support
- Aggressive
fluids
- Vasopressors
- Albumin
if capillary leak (STSS)
IVIG
- Indicated
in NSTI + streptococcal TSS
- Evidence:
↓ mortality
- Works
synergistically with clindamycin
10. DIFFERENTIAL DIAGNOSIS
- Cellulitis
- Pyoderma
gangrenosum (⚠ surgery worsens)
- Clostridial
myonecrosis
- Pyomyositis
- Deep
vein thrombosis
11. PREVENTION & INFECTION CONTROL
- Close
contacts of GAS NSTI
- Consider
prophylaxis in high-risk individuals
- Droplet
+ contact precautions
- Can
stop precautions after 24 hrs of antibiotics
12. PROGNOSIS
Mortality (approximate):
- Type
I NSTI: ~20%
- Fournier
gangrene: 22–40%
- Cervical
NSTI: ~22%
- Neonatal
NSTI: ~60%
Poor prognostic factors
- Delay
to surgery >24 hrs
- Age
>60
- Creatinine
>2 mg/dL
- WBC
>30,000
- STSS
- Head/neck/abdominal
involvement
TAKE-HOME MESSAGE
NSTI is a surgical diagnosis and surgical emergency
If you think it might be NSTI →
explore early
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