skin 15: necrotizing fasciitis and toxic shock-like syndrome Flashcards Preview

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necrotizing fasciitis (NF)

An uncommon life-threatening infection of subcutaneous tissue which results in necrosis of fascia, fat, tissues and vasculature with or without secondary involvement of skin and skeletal muscle but with severe systemic illness including one or more of following: shock, DIC, organ failure.


NF forms:

Type I: Polymicrobic (mixed) Form caused by facultative anaerobes and anaerobes

Type II: Monomicrobial Form

Type III: Clostridial myonecrosis, AKA Gas Gangrene


Polymicrobic (mixed) Form (Type I) Number of etiologic agents involved ranges from 5-15 and include:

*G+ cocci*: Streptococci, Staphylococci.
*Numerous facultative anaerobic and/or obligate anaerobic, G- rods* (e.g., Escherichia coli, Pseudomonas sp., etc).
A variant of type I is saltwater necrotizing fasciitis caused by the salt water agents, the vibrios.


Predisposing factors to NF Type I (FYI):

surgical procedure (esp. the bowel),
vulvovaginal infections.,
infections involving ulcers, abscesses, IVDU


Monomicrobial Form (Type II): agents

G+ cocci:
-GAS – *invasive GAS (serotype M1)*
-Peptostreptococcus sp.
-S. aureus
-mixed infections - both GAS and S. aureus

obligate anaerobic, G+ rods:
Clostridium perfringens, type A; C. septicum.

obligate anaerobic, G- rods (e.g., Bacteroides sp.).


Predisposing factors for NF Type II is mainly underlying disease (FYI):

arteriosclerotic vascular disease,
venous insufficiency,


NF Initial Presentation (within first 24 hours):
location ??

Location, regardless of etiology, is usually the extremities (esp. LE)
*Patient is acutely ill and in severe pain*
*A slowly advancing cellulitis with severe, excoriating pain (while pain is subjective, the elevated level/intensity of pain is unusual for cellulitis)*


NF "cellulitis" characteristics

Involved skin progresses from tender and warm--> shiny with diffuse
symmetrical swelling (erythema, edematous).
Infection rapidly spreads along fascial planes undermining of adjacent tissues.
A broad erythematous tract in skin along the fascial plane route may be
Muscle and overlying skin are spared.


NF Days 2-4 - During the next 24-48 hours, the infection can also progress:

The erythema of the involved skin progresses from red->purple->blue and blisters/bullae containing clear yellow fluid appear.
-subQ tissues are firm and fascial planes and muscle groups cannot be discerned by palpation. Infection to the depth of the enveloping fascia generally involves muscle (bacterial myositis + destruction of muscle).


NF: ?? may occur 4 - 5 days after the initial erythema, the areas become gangrene.
what is present in about 60% of cases??
systemic symptoms may include??

Anesthesia in the affected area
-Severe pain, blisters, bullae, and anesthesia are due to occluded blood vessels.
-Bacteremia is present in most (~ 60% of) cases.
-Marked systemic symptoms are present, may include shock and organ failure.


NF complications

Streptococci, especially GAS – STSS.
Gram-negative organisms: Endotoxic shock, DIC.
Clostridial toxemia


It is necessary to distinguish between cellulitis, NF, and myonecrosis because:

cellulitis is amenable to antimicrobial therapy.
NF and myonecrosis require both:
a. surgical intervention
b. antimicrobial therapy.


NF clues

*Abrupt onset of severe, excruciating pain* while subjective/not quantifiable, NF is 10 of 10
*Systemic toxicity*: often AMS (confusion).
*Hard, wooden feel of subcutaneous tissue, extending beyond the area of apparent skin involvement* – due to the presence of gas in tissues. *Muscle groups cannot be discerned by palpation*
Utilizing palpation of hard tissues, X-ray, CT-scan, MRI to detect gas, determine the extent of infection – necessity for surgery – see below.
If anaerobes are involved a distinctive odor of putrefaction is usually present.


NF more clues: Appearance of the tissue at surgery:

Fascia is swollen and dull gray.
Deep dissection reveals absence of pus, only a thin, brownish-colored (“dish-water”) exudate.
Extensive undermining of surrounding tissue is present.


cellulitis vs fasciitis response to abx tx

Patients with fasciitis fail to respond to antimicrobial therapy but with appropriate antimicrobial therapy for cellulitis, the patient usually improve in 24-48 h.


NF lab specimens to get:

deep tissue specimens from affected areas taken during surgery
*Warning*: Gram-stain and culture from a superficial skin lesion (if present) is not usually indicative of the deep tissue infection.


NF lab tests to do

Gs, Cx/Sn
results will often ID the true etiologic agent


NF: Approximate identification of etiologic agent(s) is required to select appropriate

G+ cocci in chains indicate GAS (aerotolerant anaerobe) or
Peptostreptococcus sp. (obligate anaerobe).
G+ cocci in clusters indicates S. aureus (facultative anaerobe).
Mixed flora suggests a polymicrobic infection.


In patients with NF and myositis caused by GAS, ?? is often (~ 50% of time) present.



NF tx

Bold resection of all necrotic material and incise fascial planes until the entire extent of infection is exposed (to the full extent of the gas penetration, not the area visibly affected)

Abx tx, based upon ID of etiologic agent(s), is prolonged (23 weeks).
-For GAS, PCN is drug of choice, but treatment failure can occur due to physiological/mechanical issues (failure of blood/vasc. to deliver PCN).

Hyperbaric oxygen.


NF mortality

Overall is high (20-30%) due to systemic involvement.
For GAS is high (30-60%), despite absence of underlying disease, use of antibiotics, dialysis, ventilators, intravenous fluids, modern surgical techniques.


Streptococcal Toxic Shock (STSS): hallmarks

Early onset of shock and organ failure.
Isolation of streptococci from a normally sterile site


STSS is ??
caused by ??

Non-menstrual toxic shock syndrome caused by lysogenized strains of S. pyogenes (GAS)
usually invasive GAS (serotype M1).
*Caused by strains that elaborate SPEs - superantigens*


occurs where??

Skin or soft tissue infection, necrotizing fasciitis, myositis (necrotizing fasciitis with or without myonecrosis is present @ 50% of the time).

POE is usually skin or mucous membrane (throat or vaginal tract).


STSS pt. with soft tissue infections tend to be ??

younger and with no underlying illness.


Elderly patients with STSS tend to have ??

GAS bacteremia with no septic (soft tissue) focus, but have underlying illness (FYI):

liver disease, alcoholism, diabetes, arteriosclerotic vascular disease.


Conditions required for STSS, same as per ??

Scarlet fever:
-Lack of neutralizing immunity in host: For STSS caused by S. pyogenes: the presence or absence of immunity to specific M-types (1, 3, 12, 28) as well as to SPEs determines the clinical syndrome, outcome of infection.
*SPEs are superantigens*


STSS symptoms which occur often 1- 2 d before the onset of other symptoms:

fever > 38.9oC (102oF) and chills
nausea and vomiting
Profuse, watery diarrhea occurs for about 1 day.


what STSS symptoms happen next?

abrupt onset of severe pain increasing to excruciating level which precedes tenderness or physical findings and usually affects the extremities (*Only if there is a focal infection, remember this disease can occur with bacteremia alone*).
-Intense mucous membrane erythema/hyperemia occurs with STSS.


Other STSS symptoms (at the time of or within 48 hours after admission):

Hypotensive shock and multi organ failure: Renal failure, CNS involvement->AMS, pulm. involvement->ARDS, Hepatic insufficiency.



STSS rash

a diffuse macular erythroderma which evolves into a scarlatiniform rash, which desquamates (particularly on palms & soles) 1- 2 w after the onset of S&S.


in STSS pt., ?? and/or ?? frequently (~50% of the time) occur.

dx based on ??
lab signs ?

NF, myositis

pts s/s
Gs, Cx/Sn of throat, blood, skin lesion/site specimens,

Lab signs: Profound left-shift in granulocyte series (band forms, AKA immature granulocytes are present in peripheral circulation).


tx of STSS

penicillin plus clindamycin


tx of STSS and NF caused by GAS:

Penicillin plus clindamycin.
+Bold resection of all necrotic material and incise fascial planes until the entire extent of infection is exposed (to the full extent of the gas penetration, not just the area visibly affected).

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