The involuting lichenoid plaque.

Progressive involution and subsequent regression of a plaque that showed the characteristic histologic findings of solitary lichen planus-like keratosis were observed in five patients. In each lesion, involution took place during a four- to eight-week period. In four patients, the lesion arose in a preexisting pigmented macule. Evolution into a plaque-like lesion coincided with the development of the inflammatory process. Origin from a preexisting lesion suggests that the lichenoid plaque is not an independent entity but a stage in the involution of the preexisting pigmented macule. The lichenoid inflammatory process resembles a delayed hypersensitivity reaction and seems to represent a cell-mediated rejection reaction.