This 40-year-old man developed non-inflammatory blisters over a period of 8 months, involving his scalp, trunk and arms. He had a few oral lesions as well. The clinician had a wide differential, including bullous pemphigoid, bullous lupus, erythema multiforme, pseudoporphyria. Bullous pemphigoid has several clinical presentations, uncommonly non-inflammatory, as in this case. The diagnosis rests on the histologic and immunofluorescence findings. Histology in this case showed little inflammation, but eosinophils were readily found. The diagnosis was confirmed with immunofluorescence, showing heavy linear IgG and C3 along the epidermal basement membrane. The antigens, BP230 and BP180, are related to the hemidesmosome. The cell-poor variant of bullous pemphigoid is realtively uncommon. The differential diagnosis would include other pauci-inflammatory subepidermal vesicobullous dermatoses, such as the porphyrias, trauma, and epidermolysis bullosa acquisita (EBA). Immunofluorescence studies should lead to the correct diagnosis, as in this case. Salt-split skin analysis may be necessary to rule out EBA.
At higher power, several eosinophils are found within the sparse infiltrate. Although the papillae show features of "festooning", hyalinization of vessels characteristic of porphyria cutanea tarda are not seen.