Necrotising fasciitis

The college loves this condition, and it crops up rather regularly.

• Question 27 from the first paper of 2021 (Group A Strep and diagnosis of necrotising fasciitis)
• Question 2 from the second paper of 2016 (Group A Strep and diagnosis of necrotising fasciitis)
• Question 25 from the first paper of 2016 (a diabetic leg)
• Question 3.2 from the first paper of 2014 (necrotising fasciitis of the abdominal wall)
• Question 24 from the first paper of 2011 (another diabetic leg)
•  Question 14.1 from the second paper of 2010 (Fourniers)
• Question 25.1 from the first paper of 2009 (necrotising fasciitis of the abdominal wall)
• Question 1 from the first paper of 2001 (a non-diabetic leg

The significance of Group A Streptococci (GAS)  in necrotising fasciitis

Without digressing into deep dark microbiology, one may summarise the issues in the following manner:

• S.pyogenes is the sole member of the Lancefield Group A. The use of the term GAS has generally  been superceded by more advanced methods of classification, as the number of streptococci species has massively exploded in the last thirty years.
• S. pyogenes produces enzymes such as hyaluronidase, which digest the fascia.
• It also produces superantigen toxins, which lead to streptococcal toxic shock syndrome.
• Most S.pyogenes infections are sensitive to benzylpenicillin
• Large doses may be required due to the Eagle effect

Risk Factors for Necrotising Fasciitis

Comorbid conditions Immunosuppression Diabetes Chronic disease Corticosteroids Malnutrition Age > 60 Intravenous drug use Peripheral vascular disease Renal failure Underlying malignancy Obesity

Aetiological factors Blunt or penetrating trauma Soft tissue infections Surgery Intravenous drug use Childbirth Burns Muscle injuries

Diagnosis of necrotising fasciitis

The definitive resource for this is probably Wong et al (2005). However, much of the summary below actually comes from the 1995 article by McHenry et al, and represents the historical and clinical features found in a retrospective case series of necrotising fasciitis patients.

Features of history

• Rapidly develping symptoms
• Reasonably young patients
• Previously healthy
• History of minor trauma, eg. scratch, bruise
• Initial injury is frequently trivial and blunt rather than penetrating
• Intense pain and tenderness over the involved skin and underlying muscle
• Pain is out of proportion to physical findings
• Risk factors may be apparent: diabetes, alcoholism, obesity, steroid use.
• Usually, the use of NSAIDs is reported (Aronoff et al, 2003)

Features of physical examination

• At the earliest stages, necrotising facsiitis is indistinguishable from severe cellulitis.
• Severe pain on palpation is an early feature
• The affected tissue is oedematous and has a "wooden, hardened feel"
• Erythema is present early.
• Skin "blebs", i.e. bullae with clear fluid develop as skin ischaemia progresses, and these become haemorrhagic in a late presentation
• Crepitus on palpation is another late sign
• Decreased sensation of the overlying skin develops late in the course, and the skin may appear clearly gangrenous

Biochemical features

• Acute renal failure
• Coagulopathy; DIC
• Raised inflammatory markers (WCC, CRP)
• Hypocalcemia
• Metabolic (lactic) acidosis
• Rapid antigen detection test for Group A Strep: this is mainly for pharyngitis (Gerber et al, 2004), but has been used to achieve a rapid diagnosis of lifethreatening GAS soft tissue infection (Ault et al, 1996)
• "Streptozyme" tests; which, according to a 2009 book chapter by Gould and Reeves are "generally not helpful except as paired acute and convalescent titres", which means the patient will be long dead if you wait for these to become diagnostic of necrotising fasciitis. Oh well, here'es a list of theem anyway, directly from Question 2 from the second paper of 2016
  • Anti-streptolysin (ASO) 
  • Anti-hyaluronidase (AHase) 
  • Anti-streptokinase (ASKase) 
  • Anti-nicotinamide-adenine dinucleotidase (anti-NAD) 
  • Anti-DNAse B antibodies

Radiological appearance

• CT findings:
  • Deep fascial thickening
  • Contrast enhancement
  • Fluid and gas in the soft tissue planes in and around the superficial fascia
• Ultrasound findings:
  • Thickening and distortion of the deep fascia
  • Fluid collections along the deep fascia
• MRI findings
  • Deep fascial thickening
  • Deep fascial fluid collections
  • Hyperintense T2W signal within the muscles

Surgical findings

• The presence of grayish necrotic fascia
• A lack of resistance to blunt dissection: i.e. the normally firmly adherent superficial fascia just sort of falls apart under gentle traction your hands.
• Lack of bleeding of the fascia during dissection
• The presence of foul smelling ‘dishwater’ pus.

Histopathology

• The histologic criteria for diagnosis as described by Stamenkovic and Lew (1984) were as follows:
  • Necrosis of the superficial fascia
  • Polymorphonuclear infiltration of the dermis and fascia
  • Fibrinous thrombi of arteries and veins coursing through the fascia
  • Angiitis with fibrinoid necrosis of arterial and venous walls
  • Presence of microorganisms within the destroyed fascia and dermis
  • An absence of muscle involvement.

Microbiology

• S.pyogenes is frequently the organism found on tissue culture
• Blood cultures are also frequently positive

Management of necrotising fasciitis

The key factors in its management:

• Source control
• Broad spectrum antibiotics (usually people reach for a carbapenem)
• Clindamycin (or any lincosamide)
• IV immunoglobulin
• Hyperbaric oxygen

Source control

• Debridement is the single most useful management strategy.
• Surgical debridement should be early and aggressive (this improves survival, as has been demonstrated in multiple studies).
• In fact, a delay in surgery of over 24 hours seems to increase the relative risk of mortality by 9.4 (i.e. the mortality is ten times greater if you wait another day).

Broad-spectrum antibiotics

• The addition of clindamycin is well supported - particularly with Group A streptococci, where it inhibits the bacterial synthesis of endotoxin.
• A nice retrospective audit of necrotising fasciitis patients from Victoria (Australia) had revealed that patients who were treated with clindamycin, though on average sicker, were much more likely to survive (their mortality improved from 39% to 15%).
• Other antibiotics would be needed, as clindamycin alone is not going to be sufficiently rapid in its bactericidal activity. The other antibiotic choices should cover broadly, and hit both gram positives and gram negatives in aerobic and anaerobic environments. They should be especially active against rapidly replicating organisms, and should be capable of penetrating deep into devitalised tissue or fluid cavities. Meropenem hits all the right notes, and is a reasonable first choice. Vancomycin is often added, mainly because one of the possible differentials is a nasty S.aureus mutant of some sort (for example the Panton-Valentine leukocidin variant). 

IV immunoglobulin

• IV immunoglobulin is a valid strategy in streptococcal toxic shock syndrome; though the investigators of the linked study didn't reach statistical significance in their primary endpoit (mortality), they did note a significant decrease in organ failure scores in the IVIG group.
• Encouraged by such evidence, people have also used polyspecific immunolgobulin to manage necrotising fasciitis, or to moderate its systemic effects, to be more precise. In actual fact, the abovelinked study features patients whose surgical management was conservative, and of whom the majority did have toxic shock syndrome anyway.
• The already-mentioned retrospective audit from Victoria had also suggested that people with severe soft tissue infections benefit from IVIg irrespective of whether they ahve toxic shock syndrome or not. The addition of polyspecific immunoglobulin to clindamycin reduced mortality from 15% to 7%, even though these patients were on average sicker, with more organ dysfunction.

Hyperbaric oxygen

• The college answers to their necrotising fasciitis questions make one think that a referral to a hyperbaric centre is a mandatory part of management. However, this management strategy historically did not seem to reduce either mortality or the number of debridements. Some encouraging recent data suggests that they were doing it wrong in the 1990s, and modern hyperbaric oxygen therapy seems to be associated with a 50% reduction in mortality (from 9.4% to 4.5%). However, in spite of such findings, experts remain devoid of enthusiasm, and the recent (2015) Cochrane meta-analysis did not find any trials which might have met its inclusion criteria. All in all, hyperbaric oxygen remains a brilliant treatment looking for a disease.

Necrotising fasciitis of the abdominal wall: a specific scenario

For some reason this keeps coming up in the exam (Question 25.1 from the first paper of 2009 and Question 3.2 from the first paper of 2014). Specifically, the college keeps asking about the Gram-positive rods in the blood culture (it turns out to be a Clostridium species).

According to an authoritative source, "postoperative necrotizing fasciitis of the abdominal wall is usually caused by peritonitis in patients who have undergone multiple procedures for complications of emergency laparotomy".

However, the typical case will present as a polymicrobial zoo, and whereas Clostridium species will likely flourish in the smelly pockeds of avascular fat necrosis, it is unlikely that they will be found in the blood culture, particularly as the blood is so well oxygenated (much of the time). It is more likely that Clostridium perfringens would the sole organism in the cultures of a patient with gas gangrene of the abdominal wall. If the college mentioned subcutaneous emphysema of the abdominal wall, there would be no guesswork involved in this question. This is supported by an article from 1966 (back in the day when surgeons actually palpated people's abdomens instead of scanning them). It reports on ten patients; nine had proper crackly gas gangrene due to C.perfringens or C.multifermentans. One patient with a C.tertium infection only had abdominal wall cellulitis, just like in the college question.

Cancer-related perforations followed by necrotising fasciitis of the abdominal wall do exist in case report literature. One case from the UK reported early debridement so aggressive that it left some small bowel and kidney on show (that time, β-haemolytic strep was responsible).