Q: In necrotising fasciitis/myositis, which of the following is most reliable/sensitive? 

A) Plain x-ray 
B) CT scan without contrast 
C) MRI 
D) Ultrasound 
E) PET scan


Answer: B

Contrary to expectation, MRI is not as useful as CT scan without contrast in the diagnosis of necrotising fasciitis/myositis as MRI's over sensitivity overestimates deep tissue involvement and cannot provide demarcation between necrotizing cellulitis and deeper infection!

Ultrasound lacks sensitivity as soft tissue swelling from any cause is hard to distinguish from necrotising etiology.

PET scan has no role in the diagnosis of necrotising fasciitis/myositis, and is used by autor of this MCQ to fill up five choices :)

Clinical exam and surgical approach is still the gold standard in the diagnosis of necrotising fasciitis/myositis.



References:

1. Anaya DA, Dellinger EP. Necrotizing soft-tissue infection: diagnosis and management. Clin Infect Dis 2007; 44:705.

2. Zacharias N, Velmahos GC, Salama A, et al. Diagnosis of necrotizing soft tissue infections by computed tomography. Arch Surg 2010; 145:452. 

3. Schmid MR, Kossmann T, Duewell S. Differentiation of necrotizing fasciitis and cellulitis using MR imaging. AJR Am J Roentgenol 1998; 170:615.