Necrotizing Fasciitis - A diagnostic challenge

Necrotizing Fascitis is characterized by fulminant, extensive soft tissue necrosis, systemic toxicity, and high mortality. Early in the course, the disease can appear deceptively benign and may look like cellulitis. 

Prompt diagnosis of necrotising fasciitis (NF) and early intervention reduces mortality and amputation rates. Unfortunately NF is misdiagnosed in the initial stages of the disease in almost 75% of the patients. Because thrombosis of large numbers of capillary beds must occur before skin findings develop, early infection has little overlying skin changes to indicate the extent of infection. 

Patients classically present with the triad of pain, swelling and erythema. The most consistent feature of early NF is that the pain is out of proportion to the swelling or erythema. Other important features that make NF likely are:

• Tenderness extending beyond the apparent involved area 
• Indistinct margins of involvement 
• Absence of lymphangitis  (because the infection is in the deep fascia and not in the skin)
• Rapidly progressive despite the use of antibiotics 
• If the patients looks too sick for cellulitis
• Bleb/Bullae, Crepitus (Though you cannot not rule out NF in their absence)

Usually fever or pain develops first followed by the cellulitic changes. The classic textbook picture of hemorrhagic bullae, crepitus, and skin necrosis often does not occur until day 5. 

Risk factors: 

Advanced age

Diabetes mellitus

Alcoholism

Peripheral vascular disease, Heart disease

Cenal failure

HIV, Cancer (Immunocompromised state)

NSAID use

Decubitus ulcers, chronic skin infections

IV drug abuse

Note: Although risk factors are frequently present, the disease can occur in healthy young patients. 

POCUS (Point of care ultrasound)
This is a great tool that can aid to diagnose cellulitis, NF or underlying collection/abscess. 

1. Cellulitis: 
   1. Diffuse thickening of subcutaneous layer, Echogenecity +
   2. Hypoechoic septae between the fat and connective tissue : “cobble-stone” appearance - See the image below
      
      
      
      
      
      
      
      
      
      
      
2. Abscess:
   1. Variable appearance from anechoic to irregularly hyperechoic, internal echoes; may find hyper echoic sediment, septae or even gas!
   2. Posterior acoustic enhancement
   3. “Squish sign” with compression: ability to induce motion in the material with
      palpation/pressure
3. Necrotizing fasciitis: 
   1. Marked thickening of the subcutaneous layer (i.e. cellulitis) 
   2. Layer of anechoic fluid measuring >4mm, adjacent to the deep fascia 
   3. Subcutaneous gas (acoustic shadowing and reverberation artifact) may be present 

Click on the link below to learn Soft tissue ultrasound in 17 minutes.

http://www.emergencyultrasoundteaching.com/narrated_lectures.html 

Treatment for NF:

1. Treat Sepsis (Fluids/Antibiotics)
2. Remove the focus (Debridement/Amputation) - ASAP

Key Points:

• Always think NF whenever you call it cellulitis.
• Early NF may not show classical textbook skin changes.
• If you see bullae, feel crepitus - you are dealing with NF.
• Use POCUS (Point of Care USG) for soft tissue infections.

For Further reading:

1. Yen ZS, Wang HP, Ma HM, Chen SC, Chen WJ. Ultrasonographic screening of clinically-suspected necrotizing fasciitis. Acad Emerg Med 2002;9(12):1448-51.
2. Chao HC, Lin SJ, Huang YC, Lin TY. Sonographic evaluation of cellulitis in children. J Ultrasound Med 2000;19(11):743-9. 
3. www.emergencyultrasoundteaching.com
4. Tayal VS, Hasan N, Norton HJ, Tomaszewski CA. The effect of soft-tissueultrasound on the management of cellulitis in the emergency department. Acad Emerg Med 2006;13(4):384-8.
5. Vincent LM. Ultrasound of soft tissue abnormalities of the extremities. Radiol Clin North Am 1988;26(1):131-44.
6. Squire BT, Fox JC, Anderson C. ABSCESS: applied bedside sonography for convenient evaluation of superficial soft tissue infections. Acad Emerg Med 2005;12(7):601-6.