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.
types of necrotizing fasciitis
From a practical standpoint, necrotizing fasciitis can be divided into a few types. Clinically this distinction may not be obvious, but sometimes it is helpful.
Necrotizing fasciitis may also rarely occur due to monomicrobial infection with other pathogens as listed below. Some classifications include these organisms within Type II necrotizing fasciitis. Fortunately, these infections are rare and should generally respond to the usual broad-spectrum therapy for necrotizing fasciitis described later in the chapter.
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)
skin examination: early findings are less specific
Pain is generally the most useful finding (although it's only ~90% sensitive).
Pain is often out of proportion to external appearance.
Pain is a relatively early finding, perhaps the most useful finding overall.
Pain may extend beyond superficial erythema (unlike cellulitis).
Pain can be absent or muted in patients with diabetic neuropathy, or in necrotizing fasciitis following trauma, surgery, or childbirth (in whom the pain may be misattributed to the surgery or trauma).
Erythema, which can appear similar to cellulitis.
Edema may extend beyond superficial erythema.
Tissue may have “woody” induration.
skin examination: late findings are more specific
⚠️ Absence of late skin findings should not dissuade you from pursuing a diagnosis of necrotizing fasciitis.
Subcutaneous emphysema (sensitivity is poor, only ~25%).
Purple discoloration, or a bruised appearance.
Blistering or bullae may occur.
These may become hemorrhagic (yielding characteristic violaceous bullae – an extremely worrisome finding).
Eventually this evolves into frank necrosis with sloughing of the skin.
With skin necrosis, pain will eventually transition to numbness.
Patients may look fine initially, or they may appear quite toxic.
Systemic manifestations can include delirium, vomiting/diarrhea, and frank septic shock.
🤒 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 here.
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.
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, within the appropriate clinical setting.
The sensitivity isn't great (<30% overall).
Gas will not occur with aerobic monomicrobial necrotizing fasciitis (e.g., group A streptococcal, type II necrotizing fasciitis).
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 often useful to compare affected skin to contralateral or unaffected areas.
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.
CT scan is faster and easier to interpret (especially contrast-enhanced CT scan).
Although MRI performs well on paper, for critically ill patients CT scan is generally more realistic and useful.(33278180)
contrast enhanced CT scan
Gas may be visualized in tissues.
Fascial thickening, fluid in fascia.
Stranding of adjacent fat.
Lack of fascial enhancement with contrast.(31584343)
Performance of CT scan
Contrasted CT scan has a sensitivity of ~94% and a specificity of ~77%.
Performance will vary depending on how early the necrotizing fasciitis is suspected. Thus, these numbers are averages which 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.
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).
Exploration should be performed when diagnosis remains in doubt.
Note that none of the above tests has 100% sensitivity, so the only way to avoid missing necrotizing fasciitis is to surgically explore borderline cases.
Unfortunately, initial exploration may be falsely negative in up to 14% of cases, with necrotizing fasciitis being diagnosed upon re-exploration.(32394067)
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 which may support the presence of necrotizing fasciitis:
Fascial layers easily split apart.
“Dishwater” drainage is seen (although there is typically no frank purulence).
The fascia may appear necrotic (dull and grey).
If necrotizing fasciitis is diagnosed, the patient should be transferred to the OR immediately for formal debridement. Alternatively, if necrotizing fasciitis is excluded, then the skin can be closed with a few sutures.
An example of surgical exploration is on YouTube here.
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.
Patients with streptococcal necrotizing fasciitis (Type II) often simultaneously have toxic shock syndrome.
The presence of type II 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 type II 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 type II necrotizing fasciitis, but not in other types of necrotizing fasciitis.
More on IVIG for the treatment of toxic shock syndrome here.
Some forms of necrotizing fasciitis are caused by anaerobic bacteria (especially clostridial species). Oxygen is toxic to these bacteria. Therefore, administration of higher levels of oxygen could increase tissue oxygen levels and thereby discourage the spread of these anaerobic bacteria.(33278180)
Oxygen therapy is probably pointless for Type II necrotizing fasciitis due to group A streptococci (which are aerobic).
hyperbaric oxygen therapy
This might theoretically be useful for anaerobic necrotizing fasciitis, but isn't supported by high-level evidence. Additionally, most hospitals lack this therapy. Furthermore, it may be logistically challenging or impossible to perform adequate therapy within a hyperbaric chamber.
Currently available evidence doesn't support interhospital transfer of critically ill patients with necrotizing fasciitis for the purpose of receiving hyperbaric oxygen therapy.
providing a higher FiO2 level
In centers which lack hyperbaric oxygen, providing a higher FiO2 (e.g., ~90%) is a simple intervention that could be beneficial.
Among intubated patients, this is achieved by simply increasing the FiO2 on the ventilator.
Among nonintubated patients, this can be achieved by either:
1) Using high-flow nasal cannula (set to 100% FiO2 and a moderate flow rate).
2) Simultaneously applying the combination of a nonrebreather face mask plus a nasal cannula underneath, both set to 15 liters/minute oxygen flow.
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.
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15849047 Norrby-Teglund A, Muller MP, Mcgeer A, Gan BS, Guru V, Bohnen J, Thulin P, Low DE. Successful management of severe group A streptococcal soft tissue infections using an aggressive medical regimen including intravenous polyspecific immunoglobulin together with a conservative surgical approach. Scand J Infect Dis. 2005;37(3):166-72. doi: 10.1080/00365540410020866 [PubMed]
23846850 Yue J, Dong BR, Yang M, Chen X, Wu T, Liu GJ. Linezolid versus vancomycin for skin and soft tissue infections. Cochrane Database Syst Rev. 2013 Jul 12;(7):CD008056. doi: 10.1002/14651858.CD008056.pub2 [PubMed]
29672405 Fernando SM, Tran A, Cheng W, Rochwerg B, Kyeremanteng K, Seely AJE, Inaba K, Perry JJ. Necrotizing Soft Tissue Infection: Diagnostic Accuracy of Physical Examination, Imaging, and LRINEC Score: A Systematic Review and Meta-Analysis. Ann Surg. 2019 Jan;269(1):58-65. doi: 10.1097/SLA.0000000000002774 [PubMed]
31284035 Peetermans M, de Prost N, Eckmann C, Norrby-Teglund A, Skrede S, De Waele JJ. Necrotizing skin and soft-tissue infections in the intensive care unit. Clin Microbiol Infect. 2020 Jan;26(1):8-17. doi: 10.1016/j.cmi.2019.06.031 [PubMed]
31584343 Tessier JM, Sanders J, Sartelli M, et al. Necrotizing Soft Tissue Infections: A Focused Review of Pathophysiology, Diagnosis, Operative Management, Antimicrobial Therapy, and Pediatrics. Surg Infect (Larchmt). 2020 Mar;21(2):81-93. doi: 10.1089/sur.2019.219 [PubMed]
32323044 Fozard J, Shafer K, Kehrl T. Sonographic exploration for fascial exploration (SEFE) in necrotizing fasciitis: a case report. Ultrasound J. 2020 Apr 22;12(1):24. doi: 10.1186/s13089-020-00168-5 [PubMed]
32394067 Urbina T, Madsen MB, de Prost N. Understanding necrotizing soft tissue infections in the intensive care unit. Intensive Care Med. 2020 Sep;46(9):1739-1742. doi: 10.1007/s00134-020-06071-w [PubMed]
33278180 Eckmann C, Montravers P. Current management of necrotizing soft-tissue infections. Curr Opin Infect Dis. 2021 Apr 1;34(2):89-95. doi: 10.1097/QCO.0000000000000700 [PubMed]