Atypical bullous disease showing features of both erythema multiforme and bullous pemhigoid

A 78-year-old man presented with multiple, centrifugal erythema, which tended to coalesce, producing polycyclic configurations. The patient developed an annular, narrow blister that was always visible along the margin of the erythema. Histology of a biopsy specimen revealed hydropic degeneration of basal cells, exocytosis of lymphoid cells, and subepidermal blister with necrosis of individual keratinocytes in the blister roof. Direct immunofluorescence studies showed a weak IgG deposition at the basement membrane zone, in a linear fashion, which was confined to the outer side of the blister. Immunoblotting of the patient's serum with human epidermal extract demonstrated circulating antibodies, which reacted to 230 kDa BP antigen 1. These findings suggest that this case is characteristic of both erythema multiforme and bullous pemphigoid and it seems likely that this condition could be a manifestation of epitope spreading, although the exact process in the development of immunological disturbances could not be elucidated.