The main finding here is that the epidermis has been separated from the basement membrane it is usually attached to. This is called subepidermal acantholysis. This forms a bulla between the epidermis and the basement membrane. This bulla is filled with low-protein fluid and eosinophils.
Diagnosis: Bullous pemphigoid
The subepidermal acantholysis is due to autoantibodies binding the hemidesmosomes that usually bind the keratinocytes to the basement membrane. This can be visualized on immunofluorescence as linear deposition of antibodies along the basement membrane.
46. Melanocytic nevus and superficially spreading melanoma