PUVA-induced lichen planus pemphigoides.

A 72-year-old woman had suffered from parapsoriasis en plaque (large plaque type) controlled by topically applied psoralen ultraviolet A (PUVA) therapy. The parapsoriasis lesions gradually disappeared, but numerous tiny red papules with pruritus appeared over the forearms and lower legs 120 days after starting PUVA therapy. These papules developed to form violaceous plaques. Histological findings demonstrated the characteristics of lichen planus. Two months later, tense bullae developed on the plaques and on uninvolved skin of the limbs. These were subepidermal, with linear deposits of IgG and C3 along the basement membrane zone (BMZ) in immunofluorescence of peribullous skin, and immunodeposits of type IV collagen along the floor of the bullae. We therefore, diagnosed lichen planus pemphigoides (LPP). Using systemic and topical steroid therapy, the lesions rapidly resolved and there has been no recurrence. This case suggests that the combination of basal cell injuries caused by chronic inflammation and PUVA therapy could expose BMZ components to autoreactive lymphocytes and induce LPP.