Bullous pemphigoid. Autoimmune response to hemidesmisonal proteins at the epidermal-dermal junction. Specifically in the basement membrane.
Bullous pemphegoid. - likely due to many etiologies such as drugs, infections and autoimmune dx. Pemphigus appears to be more destructive and hemorrhagic w Nikolskys sign (+) - though not pathognemonic but highly suggestive.