Diagnosis
On a physical exam, pemphigus vulgaris has flat bullae and a positive Nikolsky's sign. The gold standard for diagnosis is a punch biopsy from the area around the lesion and examining it with direct immunofluorescent staining, showing acantholytic cells. These can also be seen on a Tzanck smear. These cells are basically rounded, nucleated keratinocytes formed due to antibody mediated damage to cell adhesion protein: Desmoglein.
Pemphigus vulgaris is easy to confuse with impetigo and candidiasis. IgG4 is considered pathogenic. The diagnosis can be confirmed by testing for the infections that cause these other conditions, and by a lack of response to antibiotic treatment. Eosinophils tend to be found within the blisters and provide an important clue supporting bullous pemphigoid as the diagnosis.
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