Soft Tissue & Bone Infections
Necrotizing fasciitis (nec fasc) is a life-threatening necrotizing infection that should always be on your radar. As the name suggests, pathogens have accessed the fascial plane and can literally slide between the subcutaneous fat and the underlying muscles. This is bad news.
Nec fasc has two main types: Type I is polymicrobial with all sorts of microbes, including aerobic and anaerobic gram-positive and gram-negative organisms (think Fournier’s gangrene as well as Clostridial myonecrosis with C. perfringens). Type II is monomicrobial and typically due to Strep pyogenes (although Staph aureus, Vibrio vulnificus and group B streptococci are some other key players).
Nec fasc usually also occurs due to some skin barrier breakdown, but a portal of entry is not always found. It’s also much more common in patients with comorbidities such as diabetes, liver disease, malignancy, immunosuppression and injection drug use, but even healthy patients are at risk. Initially, the skin findings may resemble cellulitis but significant systemic symptoms such as hypotension, fever, altered mental status and “pain disproportionate to exam” should clue you in to a necrotizing process. The skin changes occur rapidly and may become bullous or ecchymotic; some patients will lose sensation due to cutaneous nerve damage. On exam, “woody” induration and crepitus are classic.
Imaging (MRI is most sensitive) can help establish the extent of infection, and blood cultures can help identify the causative organism, but the gold standard of both diagnosis and treatment is surgical exploration. Get surgery on board as soon as possible!
Empirically, antibiotics should cover both potential types of nec fasc—give:
1) Vancomycin IV (to cover MRSA) and
2) Pip-tazo IV (to cover gram-positives, gram-negatives and anaerobes) and
3) Clindamycin IV (NOT for “double anaerobic coverage,” but to inhibit toxin production by group A strep and Clostridium species; this is adjunctive)
Practical Pearl
How long is antibiotic therapy for necrotizing fasciitis?
Clindamycin is typically only continued until the patient is clinically and hemodynamically stable for 48-72 hours (that is, not in septic shock).
Duration of therapy is unpredictable but in general, we tailor antibiotics based on surgical culture results and keep antibiotics on at least until the patient is clinically stable and there is healthy granulation tissue at all debridement sites (i.e., no more surgical debridement is needed.) This can be anywhere from 2 weeks to a month (or more!)