The diagnosis of NF is initially based solely on clinical findings, which vary significantly between patients. The differential diagnosis includes cellulitis of dental origin, erysipelas, deep neck-space infections, and gangrenous necrosis due to Clostridium.
Pain out of proportion to other clinical findings is an important clue to the diagnosis of this condition. A careful examination should be undertaken for evidence of an entry site such as a small break or sinus in the skin, from which a grayish, turbid semipurulent material may be expressed ("dishwater pus"), as well as for the presence of skin changes (brawny hue or brawny induration). Due to the presence of gas-producing organisms, detection of subcutaneous air is a classic finding in NF, although this finding is not always detectable on x-ray imaging. Although radiologic evaluation is controversial and recommended only for patients in whom the disease is not seriously considered, due to the delay in surgical intervention, computed tomography of the head and neck is the imaging study of choice to confirm the presence of gas and provide detailed anatomical information (18). A critical element of diagnosis is a high clinical index of suspicion for the infection, given that subcutaneous or radiologic changes may not readily be apparent early in the disease and may delay the required early, aggressive surgical intervention. During the procedure, a confirmatory Gram stain should be performed on tissue fluid.
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