A patient presents with a red swollen leg and systemic signs of sepsis. You suspect necrotising fasciitis.  How will you confirm the diagnosis and what are the priorities of management?

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College Answer

This question was generally well covered but candidates often failed to consider history and examination  as  part  of  the  diagnostic  process.  Necrotising  fasciitis  is  an  uncommon  soft  tissue infection, which is characterised by widespread fascial necrosis with relative sparing of skin and underlying muscle. It may be caused by a single virulent bacterium usually from skin or mixture of bacteria usually enteric.

The question was in two parts:

(a)        Confirm the diagnosis. Suspicion will be raised by history, examination and confirmed by investigations and surgical exploration. There may be a history of inciting event such as animal or insect bite, penetrating trauma, abdominal surgery, appendicitis, perineal surgery or trauma.

Early examination reveals an erythematous, tender, swollen area accompanied by local pain and fever.   The skin becomes smooth, shiny and tensely swollen. In a few days the skin darkens to a patchy, dusky blue as blisters and bullae develop. Frank gangrene may then develop.

Investigations reveal non-specific leukocytosis and positive blood cultures. X-ray may reveal subcutaneous air but early surgical exploration will confirm the diagnosis in the absence of resistance of normally adherent fascia to blunt dissection. There is a watery, thin (sometimes foul-smelling) pus in the subcutaneous space.

Other adjuncts include CT, MRI and full thickness biopsy. CT may show the subcutaneous air but MRI shows the extent of the fascial necrosis and guides limits of debridement. Biopsy helps differentiate fasciitis from cellulitis which is usually medically treated.

(b)       Management priorities are :

-     confirmation of diagnosis (history, examination, investigations)

-     resuscitation ( fluid, inotropes)

-     early and definitive surgery (the most important intervention)

-     antibiotics  to  cover  gram  positive,  gram  negative  and  anaerobic  organisms  before definitive                   cultures    are     available    (eg     ampicillin/gentamicin/metronidazole  or

clindamycin/gentamicin if penicillin allergic)

-     hyperbaric oxygen as an adjunct

Discussion

Though different in its wording, this question is functionally similar to Question 24 from the first paper of 2011, which asks the candidate to discuss the management of necrotising fasciitis in a diabetic. That diabetic also has a cellulitic thigh and features of systemic sepsis. In the Discussion section, the management priorities are outlined in a boring algorithmic fashion (A, B, C. )