Definition
Clostridial Myonecrosis
- necrotizing, gas producing infection of skeletal muscle 2° Clostridia
- life threatening & rapidly progressive
Classification
There are 3 types of bacterial gas-forming infections
1. Classical clostridial gas gangrene
- rapid onset of sepsis / couple of days
- muscle nearly always involved
- critically ill immediately following an open injury
- typically > 40° C
- pain & disorientation
- extensive myonecrosis
- brownish discharge
- extensive crepitus along the tissue planes
- requires amputation 1 joint above all involved muscle compartments & high dose penicillin
2. Streptococcal myonecrosis
- tissue-plane infection
- clinical evolution is slower / 3 - 4 days
- patients are not as critically ill as those with clostridial infection
- requires excision of all involved muscle compartments combined with open wound management and penicillin therapy
3. Anaerobic Gram negative gas gangrene
- necrotizing fasciitis
- common in diabetics with open ulcers
- usually polymicrobial
- requires open debridement combined with broad-spectrum antibiotics
Epidemiology
Open Fractures
Penetrating wounds
War & Farmyard wounds
Surgical wounds - Bowel / Poor technique
Hypovascular limbs - DM / PVD
USA 1000 / year
- 0.05% of open fractures
Pathology
Need 3 things
1. Necrotic tissue - especially buttock & thigh
2 Ischaemia with low PO2
3. Contamination with Clostridium
Greatly increased by
- poor debridement
- poor antibiotics
- 1° wound closure
Clostridium perfringens
Large gram positive rod
- does not produce spores
- obligate anaerobe
Ubiquitous (present in several places simultaneously)
- 20% of patient's skin
- commensal of GIT
- faeces in high concentrations
- coil
- common in hospitals
Saprophytic
- nutrition involving uptake of organic materials obtained from dead or decaying plant or animal matter
Exotoxins
- proteolytic or sacrolytic
- most important is A-Toxin (Lecithinase)
- + Haemolysin, Collagenase, Hyaluronidase, Leukocidin, Deoxyribonuclease, Protease & Lipase
Vicious cycle
- necrotic closed wound is contaminated with clostridium
- low PO2
- production of Histotoxins
- destruction of cell wall / local tissue death
- overwhelms WBC
Pathology
Necrotic muscle
- reddish purple & friable
- becomes greenish purple
- gas in tissue
Clinical Features
History
- develops within 24 hours of closure of a deep contaminated wound
- muscle penetrating injury
Pain out of proportion to injury or procedure
- alert & anxious
- patient in fear of death
Septic shock
- pale & sweaty
- moderate fever
- tachycardia + shock
- Delerium » Coma » Death
Wound
Early
- skin swollen & white
- tense oedema & local tenderness
- serosanguineous & brown discharge
- foul or sweet odour
- ± crepitus secondary to gas
Rapid progression
- bronze discolouration
- blebs containing dark fluid
- areas of green-black cutaneous necrosis
Investigations
Clinical diagnosis
- positive blood culture in 15%
- gram-stain of exudate not helpful
- positive Nagler's test (Lecithinase turns egg yolk opaque in agar)
X-ray
Gaseous distension of muscle & fascial planes
DDx
1. Anaerobic clostridial cellulitis
- clostridial infection of necrotic soft tissue
- poorly debrided wound
- gradual onset / slight toxaemia & no pain
- slight brown, seropurulent exudate
- foul gas +++
- no muscle invasion
2. Strept. myonecrosis
- group A ß haemolytic Strep pyogenes
- " Flesh-eating bug"
- similar to Cl myonecrosis / muscle dead
- patient not as critically ill
- minimal gas
- muscle debridement / open wound management / penicillin
3. Anaerobic cellulitis / necrotizing fasciitis
- subcutaneous emphysema
- pain, swelling, and toxemia usually remain minimal
- gas production may be abundant with a foul smell
- muscle compartments are not involved
- multiple Causative organisms
- Clostridia / anaerobic streptococci / Bacteroides / gram-negative rods
- debridement / broad-spectrum antibiotics
Prophylaxis
Awareness
- early meticulous debridement
- leave wound open
Appropriate antibiotics
- Kefazol
- + Gentamicin if extensive contamination
- + Penicillin if farmyard
Management
1. Surgery
Most important
- Delay = Death
Emergency exploration
- examine muscles directly
- differentiate Myonecrosis from Anaerobic cellulitis from Necrotising Fasciitis
Appropriate debridement
- radical myoexcision
- fasciotomies
- ± amputation
2. Antibiotics
Penicillin high dose
- allergies - clindamycin
- beware penicillin resistance
- gentamycin for co-infection
High dose clindamycin
- may block Clostridial exotoxin
3. Resuscitate
Fluid loss +++
- prompt replacement
- monitor fluid balance
4. Hyperbaric O2
Controversial
- bacteriostatic
- bactericidal
Hazards
- barotrauma
- decompression sickness
- convulsions
- otitis media
Useful where trunk involved
- may decrease margin needed
- 3 ATM for 1hr TDS for 2/7
- don't delay debridement to transfer to hyperbaric chamber
Prognosis
Mortality
- WWI = 50%
- WWII = 25%
Now lower
- 50% if reaches trunk