CONTENTS

• Basics
• Types of necrotizing fasciitis
• Diagnosis
  • Clinical presentation
  • Laboratory abnormalities
  • Ultrasonography
  • Imaging
  • Surgical exploration
• Management
  • Sepsis resuscitation
  • Antibiotics
  • Surgical debridement
  • Therapy for simultaneous toxic shock syndrome
• Podcast
• Questions & discussion
• Pitfalls

---

basics

(back to contents)

---

necrotizing fasciitis basics

• The fascia is a thin layer of connective tissue beneath the skin. Infection can spread rapidly along this fascial layer. Severe infection of the fascia will occlude blood vessels passing through it, causing necrosis of the overlying skin.
• Because the fascial layer is deep, it may not be visibly obvious that there is a severe infection. In necrotizing fasciitis, the visible findings on the skin are the tip of the iceberg.
• Given its ability to spread rapidly and destroy overlying skin, necrotizing fasciitis is a life- and limb-threatening emergency.

necrotizing soft tissue infection (NSTI)

• Necrotizing soft tissue infection is a broader category of diseases that contains:
  • Necrotizing fasciitis.
  • Pyomyositis.
• Clinically, these two entities are largely interchangeable (since the vast majority of necrotizing soft tissue infections are due to necrotizing fasciitis).

---

types of necrotizing fasciitis

(back to contents)

---

Necrotizing fasciitis can be divided into a few types. Clinically this distinction may not be obvious initially, but often it is helpful.

type I: polymicrobial aerobes & anaerobes 

• Organism:
  • Often gram-positives, gram-negatives, and anaerobes.
  • E. coli and Enterococcus spp are commonly involved. (38037890)
• Gas formation:
  • There is often gas in tissue.
  • The foul odor of anaerobes may be perceptible.
• Anatomic location:
  • Following surgery or injury (e.g. postoperative wounds, diabetic ulceration).
  • Head/neck, abdomen, or ano-genital area (e.g., Fournier's gangrene).
• Epidemiology:
  • Typically affects patients with comorbidities:
    • Diabetes.
    • Alcoholism.
    • Obesity.
    • Renal failure.
• Associated findings: Septic shock.

type II: usually Group A Streptococcus

• Organism:
  • Usually monomicrobial infection with group A streptococci.
  • Less often, MRSA usually linked to a mutation in the Panton-Valentine Leukocidin gene. (38689406)
• Gas formation: No.
• Anatomic location:
  • Often involves the extremities, following minor trauma that breaks the skin.
  • May occur at sites of nonpenetrating trauma (including minor muscle sprain), if inflamed tissue is seeded following transient streptococcal bacteremia.
• Epidemiology of streptococcal necrotizing fasciitis:
  • May affect anyone (often young and healthy people). There is a seasonal peak when throat infections increase (e.g., influenza season), as this is a potential portal of bacteria entry into the bloodstream. (36252579)
  • Necrotizing fasciitis may occur without any violation of the skin, especially after blunt trauma (which may be minor). Trauma causes a small area of devitalized tissue that is hematogenously infected. (38037890) 
  • Necrotizing fasciitis may also occur following introduction of bacteria via compromised skin (e.g., varicella infection, scabies, pressure sores, eczema), surgery, or IVDU. (36252579)
  • Increased risk associated with pregnancy (e.g., postpartum surgical site).
• Associated findings:
  • Septic shock.
  • Toxic shock syndrome (e.g. vomiting/diarrhea, encephalopathy, diffuse erythroderma).

type III: Clostridium

• Organism:
  • Usually clostridium perfringens.
  • Clostridium septicum.
  • Clostridium sordelli.
• Gas formation: Often (this is “gas gangrene”).
• Anatomic location:
  • [1] Direct inoculation via penetrating trauma, intramuscular injection, or surgical wound (especially bowel surgery).
  • [2] Bacteremic spread from colon to various locations (may have multifocal infection).
• Epidemiology:
  • C. perfringens is associated with penetrating trauma, surgery, or IVDU.
  • C. septicum may spread through the bowel and into the blood, presenting as “spontaneous” infection. Usually this is due to underlying colon cancer and/or immunosuppression (e.g. neutropenia, chemotherapy).
  • C. sordellii is associated with childbirth and injection with black tar heroin. (38689406)
• Associated findings:
  • Septic shock.
  • Very high white blood cell counts (e.g., WBC >40,000). (38689406)
  • Intravascular hemolytic anemia.
  • Very rapid progression.
  • May invade tissue more deeply involving muscle and viscera.

other pathogens that can cause necrotizing fasciitis 

• Vibrio vulnificus: usually associated with liver disease, seawater exposure, or consumption of contaminated seafood.(31584343)
• Aeromonas hydrophila: usually associated with trauma occurring in fresh water.(31584343)

---

clinical presentation

(back to contents)

---

four presentations that should make you think about necrotizing fasciitis:

• Necrotizing fasciitis may manifest in a variety of ways, but four useful stimuli to consider the diagnosis are as follows: (Weingart EMCrit 378 podcast)
• [1] Skin infection plus septic shock. Cellulitis by itself doesn't cause septic shock, so something more must be going on. The differential diagnosis here usually centers around toxic shock syndrome, necrotizing fasciitis, or both.
• [2] Skin infection with worrisome exam findings (e.g., severe pain or violaceous bullae). These exam findings are explored below.
• [3] Septic shock plus focal pain (often in an extremity). Necrotizing fasciitis can involve the deeper tissue without any sign of erythema or superficial infection.
• [4] Any skin/soft tissue infection involving the scrotum. The diagnosis of Fournier's gangrene can be extremely challenging. This isn't a common location for cellulitis to occur, so there should be an extremely low threshold to involve urology.

skin examination: early findings

• Pain is generally the most useful finding (although it's only ~90% sensitive).
  • Pain is a relatively early finding, perhaps the most useful finding overall.
  • Useful attributes of pain:
    • Pain is often severe.
    • POOP (pain is often out of proportion to external appearance).
    • Pain may extend beyond superficial erythema (unlike cellulitis).
  • Causes of absent or blunted pain:
    • [a] Neuropathy (often diabetic neuropathy).
    • [b] Late stage necrotizing fasciitis (skin necrosis eventually causes numbness).
    • [c] Encephalopathy, sedation, or analgesia. (35115188)
• Erythema (71-95% sensitivity) (35115188)
  • Can mimic cellulitis.
  • Streaky lymphangitis is uncommon in necrotizing fasciitis, because lymphangitis suggests an infectious process occurring within the upper levels of the skin. (38037890)
• Edema:
  • Edema may extend beyond superficial erythema.
  • Tissue may have “woody” induration.

skin examination: late findings

• ⚠️ Absence of late skin findings should not dissuade you from pursuing a diagnosis of necrotizing fasciitis.
• Subcutaneous emphysema aka crepitus (sensitivity is poor, ~25%).
• Purple discoloration, or a bruised appearance.
• Blistering or bullae may occur.
  • These may become hemorrhagic (yielding characteristic violaceous bullae – an extremely worrisome finding). Hemorrhagic bullae are ~96% specific for necrotizing fasciitis. (35115188)
  • Eventually this evolves into frank necrosis with sloughing of the skin.

systemic manifestations are variable

• Patients may look fine initially, or they may appear quite toxic.
• 🤒 Fever is present in only ~25-40% of patients on admission. (31584343, 33278180)
• Patients with Type II necrotizing fasciitis due to group A streptococcus often have early manifestations of toxic shock (e.g. nausea/vomiting, diarrhea, fever, myalgias). The constellation of these “flu-like” systemic features plus extremity pain should be suggestive of necrotizing fasciitis plus toxic shock. More on the diagnosis of toxic shock syndrome: 📖

Fournier's gangrene

• Fournier's gangrene is a necrotizing soft tissue infection of the perineum (most often the scrotum).
• Diagnosis of Fournier's gangrene can be more challenging than evaluation of other skin areas (e.g., it is difficult to demarcate erythema or determine the presence of edema).
• ☎️ There should be a very low threshold to consult urology and obtain imaging (e.g., contrasted CT scan) if there is any concern for Fournier's gangrene.

---

laboratory abnormalities

(back to contents)

---

⚠️ Necrotizing fasciitis is not a laboratory diagnosis. Deranged labs should increase your index of suspicion, but patients can have early necrotizing fasciitis with mostly normal labs.

laboratory changes which may be seen include:

• Hyponatremia.
• Renal failure.
• CK (creatine kinase) elevation.
• Elevation of NLR (neutrophil/lymphocyte ratio).
• Elevation of CRP (C-reactive protein) and procalcitonin.
• Hyperlactatemia.
• DIC (disseminated intravascular coagulation). 📖
• (Reminder: obtain blood cultures!).

clostridial infections may cause a unique pattern of laboratory abnormalities:

• Intravascular hemolysis may occur, causing acute anemia as well as free hemoglobin in the urine (which may appear on the urine dipstick as “blood”).
• Clostridia may grow on blood cultures (don't discount gram-positive rods as “contaminant” in this context).

LRINEC score for necrotizing fasciitis

• Performance is poor.
• This is both:
  • (1) A waste of time.
  • (2) Potentially dangerous.
• Canadian guidelines recommend against using LRINEC. (38995607)

---

ultrasonography

(back to contents)

---

[1] finding of gas within the skin

• Gas within the skin may be visible as bright echogenic areas with posterior acoustic shadowing (see video above).
• The presence of gas proves the diagnosis of necrotizing fasciitis, within the appropriate clinical setting.
• The sensitivity is poor (<30% overall).
• Gas will not occur with aerobic monomicrobial necrotizing fasciitis (e.g., group A streptococcal, type II necrotizing fasciitis).

[2] abnormal fascia

• The fascia can be seen, most easily on flat areas of skin.
• Necrotizing fasciitis is suggested by thickening, distortion, or fluid in the fascia.
  • It's useful to compare affected skin to contralateral, unaffected areas.
  • >4 mm thickening suggests necrotizing fasciitis with variable sensitivity (40-80%) but a high specificity of 93%. (35115188)
• This finding isn't perfectly sensitive or specific. However, it may help calibrate your index of suspicion. In particular, if the fascia appears abnormal, this should be an impetus to more aggressively pursue the diagnosis of necrotizing fasciitis.

---

imaging

(back to contents)

---

plain radiography

• Plain films may reveal gas within the tissues, which is specific for necrotizing fasciitis. However, this is poorly sensitive (since frank gas within the tissues is a late finding which is seen only in some types of necrotizing fasciitis).
• With the use of ultrasonography, the role of plain radiography is somewhat dubious (because gas in the tissues can be established at the bedside with point-of-care ultrasonography).

contrast enhanced CT scan

• Potential findings:
  • Gas may be visualized in tissues.
  • Fascial thickening, fluid in fascia.
  • Stranding of adjacent fat.
  • Lack of fascial enhancement with contrast. (31584343)
  • Thrombosis of superficial vessels. (38689406)
  • Fluid collections deeper than 2-4 mm below the skin. (Vincent 2023)
• Performance of CT scan:
  • Contrast CT scan has a sensitivity of ~94% and a specificity of ~77%.
  • Performance will vary depending on the severity of the necrotizing fasciitis. Thus, these numbers are averages that may not apply to any specific patient.
• Roles of CT scan:
  • Occasionally, CT scan can be diagnostic (e.g., gas in tissues, thickened and nonenhancing fascia).
  • When CT isn't diagnostic, it may nonetheless help direct the surgeon to the best region to explore.

(MRI)

• CT scan is faster and easier to interpret than MRI (especially contrast-enhanced CT scan).
• Although MRI performs well on paper, for critically ill patients CT scan is generally more realistic and useful. (33278180)

---

surgical exploration

(back to contents)

---

surgical exploration

• Exploration should be performed when the diagnosis remains in doubt.
• Surgical exploration may be faster and logistically superior to CT scan. Exploration can often be performed rapidly at the bedside with local anesthesia.

how this works

• The skin is incised and the fascia explored gently with a finger or probe.
• Features that support the presence of necrotizing fasciitis:
  • Fascial layers easily split apart.
  • “Dishwater” drainage is seen (there is typically no frank purulence).
  • The fascia may appear necrotic (dull and grey).
  • Absence of bleeding.
  • Fat may appear pale and edematous. (38689406)
• If necrotizing fasciitis is diagnosed, formal debridement is necessary. Alternatively, the skin can be closed with a few sutures. An example of surgical exploration is on YouTube here.

diagnostic performance

• Initial exploration may be falsely negative in up to 14% of cases, with necrotizing fasciitis being diagnosed upon re-exploration. (32394067) In very early disease evolution or among immunosuppressed patients, the only sign of necrotizing fasciitis may be edema. (36252579)
• Obtaining a fresh frozen section of the fascia for histopathology with urgent Gram stain may improve diagnostic performance. (36252579)

---

sepsis resuscitation

(back to contents)

---

• Patients in septic shock should receive an aggressive sepsis resuscitation.
• More on sepsis resuscitation: 📖

---

antibiotics: preferred empiric regimen for necrotizing fasciitis

(back to contents)

---

[#1/3] broad-spectrum beta-lactam backbone

• Piperacillin-tazobactam 💉 is often preferred for community-acquired infections.
• Meropenem 💉 could be utilized in patients with:
  • History of resistant gram-negatives.
  • Risk factors for resistant organisms (e.g., nosocomial necrotizing fasciitis).
  • Allergy to piperacillin-tazobactam.

[#2/3] MRSA coverage, preferably with linezolid 💉

• MRSA coverage is generally recommended.
• Linezolid was superior to vancomycin in a Cochrane review of skin and soft tissue infections.(23846850, 31584343) Linezolid offers several advantages here compared to vancomycin:
  • Linezolid may suppress toxin synthesis.  This may be especially important as some Group A streptococcal and clostridial species are developing increasing resistance to clindamycin. (Vincent 2023)
  • Unlike vancomycin, linezolid is not nephrotoxic.
  • Linezolid has more reliable pharmacokinetics than vancomycin.
• If linezolid is unavailable or contraindicated, other options for MRSA coverage include vancomycin 💉 and daptomycin 💉. Further discussion on selection of a MRSA agent is here: 📖

[#3/3] clindamycin 💉 

• Dosing:
  • Typical dosing for toxin suppression is 900 mg IV q8hr.
  • One recent article recommended 1200 mg IV q6hr. (38689406)
• Clindamycin is added to suppress toxin production by either Group A Streptococci or Clostridium.
• It's debatable whether clindamycin is required in a patient who is also receiving linezolid (this is discussed further in the chapter on toxic shock syndrome here: 📖).

other antibiotic considerations:

• Suspected Vibrio vulnificus (e.g., oysters, seawater exposure): consider a combination of doxycycline plus a third or fourth-generation cephalosporin.
• Suspected Aeromonas spp. (e.g., freshwater exposure): consider a combination of doxycycline plus a fluoroquinolone.

duration of antibiotic therapy

• The duration of treatment is not well defined.
• Toxin-suppressive antibiotics (e.g., clindamycin) may be discontinued relatively early, once physiological resolution has occurred.
• Total duration of antibiotic therapy is often 7-14 days. (36252579) Experts recommend continuing antibiotics for 48-72 hours after the last surgical debridement, in the context of marked clinical improvement. (38037890)

---

surgical debridement

(back to contents)

---

• Surgical consultation must be obtained early for any patient with definite or suspected necrotizing fasciitis.
• Early debridement is generally felt to be essential, particularly in polymicrobial necrotizing fasciitis.
• Surgical management depends on the extent of necrosis. This often involves repeated procedures to resect any residual necrotic tissue. Extensive surgeries may be required (e.g., amputation, skin grafting and other techniques similar to burn surgery, a diverting colostomy to keep wounds clean).
• Among patients with necrotizing fasciitis due to group A streptococcal infection, immediate radical excision of involved tissue might not always be advisable. One case series described seven patients who were treated with high-dose IVIG (2 grams/kg/day on day one, and again on days 2-3, as needed), while debridement was delayed. (15849047) Medical management seemed to reduce the amount of skin involved, allowing for less extensive debridement afterwards. This remains highly controversial. Ultimately, this decision must be made based on collaboration between critical care, infectious disease, and surgery specialists.

---

therapy for toxic shock syndrome

(back to contents)

---

• Patients with Group A Streptococcal necrotizing fasciitis (type II) often simultaneously have toxic shock syndrome.
• The presence of Streptococcal necrotizing fasciitis may be suspected based on clinical clues:
  • Often relatively young age.
  • Lack of gas in tissues.
  • Other features of toxic shock (e.g., diffuse erythroderma, prominent gastrointestinal symptoms).
• IVIG should be considered in patients with suspected Streptococcal necrotizing fasciitis, particularly if there are signs of multiorgan failure. (33303335)
• To date, evidence supporting the use of IVIG for all comers with necrotizing fasciitis is mixed. This likely reflects that IVIG is effective in necrotizing fasciitis due to Streptococcus, but ineffective in other types of necrotizing fasciitis. (36252579)
• More on IVIG for the treatment of toxic shock syndrome: 📖

---

podcast

(back to contents)

---

Follow us on iTunes

---

questions & discussion

(back to contents)

---

To keep this page small and fast, questions & discussion about this post can be found on another page here.

• Don't get hung up on subcutaneous gas and late findings of necrotizing fasciitis (e.g., bullae, necrosis). Pain out of proportion to exam is usually the key early finding.
• If you do happen to see violaceous bullae, this is necrotizing fasciitis until proven otherwise.
• The only way to exclude necrotizing fasciitis is surgical exploration of the fascia. Labs and imaging tests can be helpful if positive, but they cannot exclude necrotizing fasciitis.
• Don't delay requesting a surgical consultation.

Guide to emoji hyperlinks

• = Link to online calculator.
• = Link to Medscape monograph about a drug.
• = Link to IBCC section about a drug.
• = Link to IBCC section covering that topic.
• = Link to FOAMed site with related information.
• = Link to supplemental media.