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.