Pemphigus and pemphigoid are most likely.
Pemphigus causes large painful long-lasting erosions (Fig. 9.3). The whole mouth can be involved, but more often it affects just the lips and buccal mucosa. Desquamative gingivitis can occur. The ulcers are large, appear without warning and last months. A biopsy may show an intraepithelial acantholysis and should not be taken from an ulcer, but from normal-appearing mucosa in an active area. Direct immunofluorescence (biopsy normal mucosa) shows antibody rimming each keratinocyte.
Cicatricial (scarring) pemphigoid affects the mucous membranes predominantly, but occasionally affects the skin too. The eyelid conjunctiva and other mucosae can also be affected; scarring often results (see Fig. 9.8). Cicatricial pemphigoid is also a cause of desqua-mative gingivitis. Biopsy shows a subepidermal bulla, and direct immunofluorescence a linear band of IgG and C3 at the dermal–mucosal junction.