A 53 yo male with a history of IV drug use presents with an abscess to his lower extremity.  He states he was injecting into the affected area 2-3 days prior to onset of symptoms.  He is well appearing but complains of severe pain and subjective fevers.  There is an exquisitely tender, fluctuant area on his anterior leg.  X-ray is shown.  What's the diagnosis?  Scroll down for answer.

Answer:  Necrotizing soft tissue infection

• High risk groups: IVDU, diapetics, those with contaminated traumatic wounds, other immunocompromised 
• Typically polymicrobial (Type 1) vs monomicrobial (Type 2, Group A strep)
• Exam findings similar to those of cellulitis with possibly crepitus, bullae, and pain out of proportion to physical appearance
• Characterized by rapid progression, systemic toxicity, high mortality
• Diagnosis may be made on plain x-ray but CT is more reliable; gas in tissues on imaging is specific but not sensitive for this disease process

• Treatment involves emergent surgical consultation for debridement as well as broad spectrum antibiotics (vancomycin with piperacillin/tazobactam or cefepime, PLUS clindamycin for inhibition of toxin production in Group A strep or Clostridial infections)
• Immunocompromised contacts of patients diagnosed with necrotizing Group A strep infection should receive prophylaxis
• See also EMDaily NSTI's

Kelly EW, Magilner D. Soft Tissue Infections. In: Tintinalli JE, Stapczynski J, Ma O, Yealy DM, Meckler GD, Cline DM. eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8e New York, NY: McGraw-Hill; 2016.