Necrotising fasciitis

Question 1

Define Necrotising fasciitis

Answer 1

Life-threatening subcutaneous infection that can extend to deep fascia but not mucle

Type 1 NF is caused by a combination of bacteria-usually an anaerobe (bacteroides/peptostreptococcus) and a facultative anaerobe (enterobacteroides, non group A Strep

Type 2 NF is a mono bacterial infection caused often by strep pyogenes alone

can also get rarer forms-aeromonas hydrophilia-with freshwater exposure
or oysters-vibrio vulnificus

Question 2

Aetiology and risk factors of Necrotising fasciitis

Answer 2

Type 1 NF is caused by a combination of bacteria-usually an anaerobe (bacteroides/peptostreptococcus) and a facultative anaerobe (enterobacteroides (e.coli, klebstriellua, enterobacter, proteus), non type 1 strep, MRSA)

Type 2 NF is a mono bacterial infection caused often by strep pyogenes (type A strep), aeromonas hydrophilia (freshwater exposure) or vibrio vulnificus (oyster exposure), and MRSA
Type 1 more common than type 2

Risk factors;
cutaneous expsorue
Exposure to other with NF
Any skin lesion
Diabetes miellitus
peripheral vascular disease
Immunucompromise
CKD, liver issues
Herpes
Steroids
IV drug use

Question 3

Epidiemology of Necrotising fasciitis

Answer 3

Unclear
Type 1 is more common than type 2
about 3.5 million cases a year-rare

Question 4

Signs and Sx of Necrotising fasciitis

Answer 4

Hx-take good Hx of exposure (freshwater/oysters/people with NF), skin trauma
Speed of infection is important

Most commonly in extermities-esp thigh-for type 2
if after surgery-most likely type 1

Hallmark is:
Severe pain or anesthesia over and area of cellulitis
Pain disproportionate to area of skin affected

skin can appear normal-
subtle changes such as leakage of fluid and oedema precede others

later-crepitus, bullae, vesicles, greyish discolouration (can go black), oedema beyond erythema

commonly, signs of sepsis (tachycardia, tachypnea, hypotense, hypothermia/hyperthermia, change in GCS) associated with cellulitis should be a massive clue

Question 5

Investigations of Necrotising fasciitis

Answer 5

FBC-WCC high (infection) or low (severe sepsis)
Left shifted (polynuclear-young)

high Urea and creat
Hyponatremia
high CRP
high serum CK and lactate

tissue/blood cultures for type1 vs type2-plus sensitivities

CT/MRI-can give better picture of nectosing area

BUT don’t delay surgery for test if urgent (esp imagery)-
can do surgical exploration before debridement