[15] Necrotising Fasciitis Flashcards
What is necrotising fasciitis?
An uncommon but life-threatening infection, defined as a necrotising infection involving any layer of the deep soft tissue compartment
What parts of the deep soft tissue compartment can be affected in necrotising fasciitis?
- Dermis
- Subcutaneous tissue
- Fascia
- Muscle
How do organisms spread to cause necrotising fasciitis?
From subcutaneous tissue along the superficial and deep fascial planes
What facilitates the spread of bacteria in necrotising fasciitis?
Bacterial enzymes and toxins
What is the effect of deep fascial infection?
- Vascular occlusion
- Ischaemia
- Tissue necrosis
What happens to superficial nerves in necrotising fasciitis?
They are damaged causing a characteristic localised anaesthesia
How are the causative organisms of necrotising fasciitis classified?
Into 4 types
What is Type 1 cause of necrotising fasciitis?
Polymicrobial infection with aerobic and anaerobic bacteria
Who is Type 1 necrotising fasciitis usually seen in?
Immunocompromised or patients with chronic disease
What is the causative organism in Type 2 necrotising fasciitis?
Group A streptococcus
Who does Type 2 necrotising fasciitis occur in?
Any age group and otherwise healthy individuals
What is the underlying cause of Type 3 necrotising fasciitis?
Gram -ve monomicrobial infection
What is a usual cause of infection Type 3 necrotising fasciitis?
Marine organisms after seawater contamination of wounds, fish fin/sting injuries and raw seafood consumption
What is an example of a marine organism that can cause Type 3 necrotising fasciitis?
Vibrio vulinficus
What causes Type 4 necrotising fasciitis?
Fungal infection
What are the risk factors for developing necrotising fasciitis?
- Skin injury
- Underlying conditions
- Varicella zoster infection (in children)
What types of skin injury can lead to necrotising fasciitis?
- Insect bite
- Trauma
- Surgical wounds
What underlying conditions can increase risk of necrotising fasciitis?
- Alcohol abuse
- IV drug abuse
- Chronic liver or renal disease
- Diabetes
- Malignancy
- Immunosuppression
- TB
What is the most common type of necrotising fasciitis?
Type 1
What percentage of necrotising fasciitis cases are caused by Type 1 infections?
70-80%
Why is early diagnosis of necrotising fasciitis difficult?
It often looks like a superficial skin infection early on
When should you have a high index of suspicion for necrotising fasciitis?
When the patient is systemically unwell or has disproportionate pain
Although it can affect anywhere, what parts of the body does necrotising fasciitis usually involve?
- Extremities
- Trunk
- Perineum
What is the usual time course for necrotising fasciitis?
Develops over a few days but potentially much quicker
In typical necrotising fasciitis development, what happens over days 1-2?
- Local severe pain
- Swelling and erythema
- Poorly defined margins
- No response to antibiotics
- Systemic illness
Why does necrotising fasciitis cause only local pain, swelling and erythema initially?
The necrotising infection is deep and so not visible
What features can distinguish necrotising fasciitis from cellulitis in the first 2 days?
- Disproportionate pain
- No response to antibiotics
- Lymphangitis is rare
- Systemic illness
What symptoms of systemic illness can be seen in the first few days of necrotising fasciitis?
- Malaise
- Tachycardia
- Fever
- Dehydration
What may be seen in days 2-4 of typical necrotising fasciitis?
- Tense oedema beyond erythema
- Possibly haemorrhagic bullae
- Discoloured skin progressing to grey necrosed skin
- Subcutaneous tissue feels wooden
- Pain progress to anaesthesia
What happens in days 4-5 of necrotising fasciitis?
- Hypotension and septic shock
- Patient becomes confused and apathetic
What is Fornier’s gangrene?
A rapidly progressing form of infective necrotising fasciitis of the perineal and genital regions leading to thrombosis of the small subcutaneous vessels and necrosis of the skin
How is necrotising fasciitis diagnosed?
Clinically
What is required if necrotising fasciitis is suspected clinically regardless of other test results?
Surgical exploration
What can sometimes be seen and act as a diagnostic tool on plain x-ray?
Gas or bullae
What macroscopic features can confirm necrotising fasciitis on surgical exploration?
- Grey necrotic tissue
- Lack of bleeding
- Thrombosed vessels
- ‘Dishwater pus’
- Lack of resistance to finger dissection
- Non-contracting muscles
What test can help to identify necrotising fasciitis if the clinical picture is uncertain?
- Blood tests
- Bedside finger test
- Microbiology
- Radiology
What blood tests can help to identify necrotising fasciitis?
- Leukocytosis
- Acidosis
- Altered coagulation profile
- Hypoalbuminaemia
- Abnormal renal function
What is a bedside finger test for necrotising fasciitis?
- 2cm incision down to deep fascia under local anaesthetic
What are the signs of necrotising fasciitis on bedside finger testing?
- Lack of bleeding
- Malodorous ‘dishwater pus’
- Lack of tissue resistance to blunt dissection
What microbiological tests can be useful for necrotising fasciitis?
- Blood cultures
- Wound swab
What radiological investigations can help to diagnose necrotising fasciitis?
- Plain X-ray
- CT
- MRI
- USS
What can be seen on a CT or -ray in some cases of necrotising fasciitis?
Tissue gas
What can be sometimes seen on MRI in necrotising fasciitis?
Extent of tissue involvement
What can sometimes be seen on USS in necrotising fasciitis?
Subcutaneous gas
Why is imaging not always useful in necrotising fasciitis?
There are often false negatives
What are the differentials for necrotising fasciitis?
- Cellulitis
- Erysipelas
- Pyoderma gangrenosum
- Limb ischaemia or compartment syndrome
- Deep vein thrombosis
- Thrombophlebitis
- Osteomyelitis
What treatment for necrotising fasciitis is essential?
Early and aggressive debridement of involved tissue
What are other important aspects of necrotising fasciitis management?
- Resuscitation
- Antibiotics
- Post-debridement surgery
Why may patients with necrotising fasciitis require resuscitation?
They are often shocked or haemodynamically unstable
Where is it often appropriate to treat patients with necrotising fasciitis?
Intensive care
What is important to ensure when surgically debriding necrotising fasciitis?
Adequate margins with no infected tissue remaining
What must happen after initial debridement of necrotising fasciitis?
Wound monitoring and daily debridement of recurring infection
When can necrotising fasciitis wounds be dressed?
Once the infection is controlled
How are necrotising fasciitis wounds closed?
By secondary suturing with or without skin grafts
What may assist healing of necrotising fasciitis wounds?
Vacuum assisted wound closing devices
How should antibiotics be started in necrotising fasciitis?
Immediately start IV broad-spectrum at high doses
What organisms should be covered by antibiotics for necrotising fasciitis?
- Streptococci
- Staphylococci
- Gram-ve rods
- Anaerobes
What support is required in necrotising fasciitis?
- Fluid
- Nutrition
When should prophylactic treatment be given to patient contacts?
When there is GAS infection
What prophylactic treatment should be given to all contacts of a person with GAS necrotising fasciitis?
Advice about symptoms and when to seek help
When should prophylactic antibiotics be given to contacts of GAS necrotising fasciitis?
- Neonates and mothers if either have invasive GAS
- Close contacts with symptoms of localised GAS
- Household if 2 or more cases of invasive GAS in 1 month
What are some symptoms of localised GAS infection?
- Sore throat
- Fever
- Skin infection
What is the first choice antibiotic in necrotising fasciitis?
- Penicillin V
What are the potential complications of necrotising fasciitis?
- Septic or toxic shock
- Tissue necrosis
- Nerve damage
- Muscle necrosis
- Skin grafting
- Reconstructive surgery
- Amputation
