A 60 year old male presents to the dermatologist with a complaint of tender blisters on his arm and flank. Physical examination reveals blisters and flaccid bullae; a few have ruptured, leaving red, sore, denuded areas. Which of the following findings would suggest the diagnosis of pemphigus vulgaris as opposed to bullous pemphigoid?

Pemphigus vulgaris is associated with chronic, severe bullae formation on the skin and oral mucosa. Mucosal lesions are extremely rare in bullous pemphigoid. This can be used clinically to guide therapy, although a skin biopsy should be taken to confirm the diagnosis. Both diseases are characterized by formation of tender bullae that can rupture,leaving red, raw areas. Pemphigus vulgaris patients eventually became febrile and lose weight, and if untreated, most will die within one year. Bullous pemphigoid lesions tend to heal and the patients do very well. This prognostic difference is an impoant distinction in dermatological medicine. Eosinophils within blisters provide an impoant clue suppoing bullous pemphigoid as the diagnosis which must be asceained with histologic examination. The vesicles in pemphigus vulgaris mostly contain rounded acantholytic keratinocytes "floating" within. IgA deposits seen with immunofluorescence on the basement membrane is characteristic of a third bullae-forming disease known as dermatitis herpetiformis. Vesicles form between the dermal-epidermal junction. The disease is associated with gluten sensitivity and celiac disease. IgG autoantibody activity is common to both pemphigus vulgaris and bullous pemphigoid. Ref: Payne A.S., Stanley J.R. (2012). Chapter 54. Pemphigus. In K. Wolff (Ed),Fitzpatrick's Dermatology in General Medicine, 8e.