Investigations

• a frozen biopsy
  1% lidocaine anaesthesia, 2 cm x 1 cm elliptical biopsies (skin and deep soft tissue) of suspected necrotising area and at another (leading edge of erythema, induration or necrosis) ^c  
  
  
• MRI ^c  

Why?

Frozen punch biopsy and MRI can help exclude necrotising fasciitis

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected necrotising fasciitis c (pre-test probability: 28%)	necrotising fasciitis (surgery)	frozen section biopsy	infinity (11 to infinity)	100%	0.0 (0.0 to 0.22)	0%
suspected necrotising fasciitis c   (pre-test probability: 28%)	necrotising fasciitis (surgery/ autopsy)	MRI	6.0 (1.0 to 36)	92%	0.0 (0.0 to 0.29)	0%