NSTI: Necrotizing Soft-Tissue Infection
NSTI stands for Necrotizing Soft-Tissue Infection—a life-threatening surgical emergency characterized by rapidly spreading infection with tissue necrosis that requires immediate surgical debridement to prevent mortality. 1
Definition and Critical Features
NSTIs are life-threatening, invasive soft-tissue infections involving any or all layers of the soft-tissue compartment, from superficial dermis and subcutaneous tissue to deeper fascia and muscle (the latter commonly called "necrotizing fasciitis"). 1
The defining characteristic is the presence of spreading infection in any soft tissue layer (skin, subcutaneous tissue, superficial fascia, deep fascia, or muscles) associated with necrosis of the involved layer(s) requiring surgical debridement. 1
Why This Matters for Mortality
Delay in diagnosis and delay in treatment directly increase mortality risk, as these infections progress to multiorgan failure. 1 The aggressive character of NSTIs demands immediate differentiation from non-necrotizing infections. 1
Classification Systems
By Risk Stratification (Most Clinically Useful)
Patients with NSTIs should be classified into two prognostic categories: 1, 2
- High risk of poor outcome
- Mild/moderate risk of poor outcome
This classification identifies patients requiring immediate surgical treatment and perioperative intensive care management. 1, 2 Severity assessment scores may be useful in the emergency room or outside the ICU for early identification. 1
By Microbiology (Less Clinically Useful)
While various classification schemes exist, the initial approach to diagnosis, antimicrobial treatment, and surgical intervention is similar for all forms—making specific variant identification less important than recognizing the need for immediate aggressive management. 1, 2
Traditional microbiologic types include: 1, 2
- Type 1: Polymicrobial
- Type 2: Monomicrobial pathogenic β-hemolytic streptococci or CA-MRSA
- Type 3: Monomicrobial gram-negative bacilli
By Anatomical Depth (Descriptive Only)
NSTIs can be described by depth: 1, 2
- Necrotizing cellulitis (dermal and subcutaneous)
- Necrotizing fasciitis (fascial component)
- Necrotizing myositis (muscular components)
However, labeling with different anatomical terms does not serve a useful purpose and may complicate management by delaying diagnosis or surgical debridement. 1
Management Principles
Surgical Management (Primary Treatment)
All NSTIs by definition require surgical debridement—this is the cornerstone of treatment. 1 Early and aggressive surgical debridement with removal of all necrotic tissue is mandatory, often requiring repeat debridement procedures. 3, 4
Antimicrobial Therapy
Broad-spectrum antimicrobial therapy should be administered empirically and reassessed pending culture and sensitivity results. 3 For severe infections with systemic toxicity, high-dose clindamycin should be included as it inhibits bacterial exotoxin production responsible for toxic shock syndrome. 3
Intensive Care Management
Patients require intensive care management with cardiovascular stabilization and monitoring, particularly those classified as high risk. 1, 3, 4
Critical Warning Signs
The necrotizing or non-necrotizing character of the infection should always be specified when classifying patients with soft-tissue infections. 1 Disproportionate pain, violaceous bullae, rapid progression, and crepitus or subcutaneous gas are critical warning signs mandating emergency surgical evaluation. 2
Common Pitfalls
The most critical error is delayed recognition of necrotizing infection. 1 Type 2 NSTIs are particularly challenging as they often present without classic signs of skin changes, subcutaneous air, and crepitus, yet spread more rapidly with higher morbidity and mortality than Type 1. 5, 6
Early prognostic evaluation is crucial to assess severity and decide treatment aggressiveness, as these infections remain an important source of patient morbidity with frequently poor clinical prognosis. 1