What are the signs and symptoms of necrotizing fasciitis?

Signs and Symptoms of Necrotizing Fasciitis

The most critical early sign of necrotizing fasciitis is severe pain disproportionate to physical examination findings, accompanied by rapid progression of symptoms and systemic toxicity. 1, 2

Key Clinical Manifestations

Early Signs (First 24-48 hours)

• Pain out of proportion to physical findings (most important early indicator) 1, 2
• Erythema and swelling without sharp margins 1
• Fever and tachycardia 1
• Wooden-hard feel of subcutaneous tissues (distinguishing feature) 1
• Warm, tender skin 3
• Initial presentation may mimic cellulitis 1

Progressive Signs (48-72 hours)

• Systemic toxicity with high temperatures 1
• Altered mental status/lethargy 1
• Hypotension and shock 1
• Edema extending beyond the area of erythema 1
• Skin discoloration or gangrene (70% of cases) 1
• Bullous lesions or hemorrhagic bullae 1, 3
• Anesthesia of involved skin (due to destruction of superficial nerves) 1
• Crepitus (in gas-forming infections) 2

Anatomical Presentation

• 80% of cases show visible progression from a skin lesion 1
• The initial lesion is often trivial (minor abrasion, insect bite, injection site, or boil) 1
• 20% of patients have no visible skin lesion 1
• Broad erythematous tract may be visible along the route of infection 1
• Subcutaneous tissues become firm, with fascial planes and muscle groups indiscernible by palpation 1

Diagnostic Clues

• Failure to respond to initial antibiotic therapy 1
• Probing the edges of an open wound with a blunt instrument permits ready dissection of superficial fascial planes beyond wound margins 1
• At surgery, fascia appears swollen and dull gray with stringy areas of necrosis and thin brownish exudate 1
• Extensive undermining of surrounding tissues without true pus 1

Laboratory Findings

The Laboratory Risk Indicator for Necrotizing infection (LRINEC) score may help predict NSTI presence, with points assigned for:

• C-reactive protein > 150 mg/L
• WBC count > 15,000/μL
• Hemoglobin < 13.5 g/dL
• Serum sodium < 135 mmol/L
• Serum creatinine > 1.6 mg/dL
• Serum glucose > 180 mg/dL 1

However, recent evidence shows LRINEC lacks sensitivity for diagnosis 1.

High-Risk Populations

Increased suspicion is warranted in patients with:

• Diabetes mellitus
• Alcoholism
• Immunocompromised states
• Recent varicella infection
• History of minor trauma or insect bites 2, 4

Common Pitfalls in Diagnosis

1. Delayed recognition: Early diagnosis is missed or delayed in 85-100% of cases 5
2. Confusion with cellulitis: Initial presentation often mimics simple cellulitis 1
3. Reliance on skin findings: Primary pathology is in the deep fascia, with skin manifestations appearing later 3
4. Waiting for classic signs: By the time skin necrosis and crepitus appear, infection is advanced 2

Clinical Pearls

• The diagnosis of necrotizing fasciitis is primarily clinical 1
• Imaging studies should not delay surgical consultation and intervention 1
• A small exploratory incision may be necessary to confirm diagnosis when suspicion is high 2
• The wooden-hard feel of subcutaneous tissues distinguishes fasciitis from cellulitis or erysipelas 1

Remember that early recognition and aggressive surgical intervention are critical for reducing mortality, as delays in diagnosis correlate with poor outcomes 6.