Benign lichenoid keratosis.

The microscopic spectrum of benign lichenoid keratosis (BLK) was studied by examination of 30 examples. BLK consists of a segment of hyperplastic epidermis accompanied by a lymphoid infiltrate in the papillary dermis. Although termed "lichen planus-like," saw-tooth acanthosis predominated in only seven lesions, whereas irregular acanthosis was widespread in 23. The infiltrate had both a band-like (lichenoid) and perivascular arrangement, but a lichenoid appearance predominated in only half the specimens. Liquefaction of the basal layer was widespread, and hydropic change often involved the midepidermis. Mild cytologic atypicality was present in each case, but other features of actinic keratosis were lacking. Changes of senile lentigo were observed adjacent to 17 lesions. Partial involution was present in several cases. BLK often is confused clinically with a variety of other cutaneous tumors. Nevertheless, the diagnosis usually can be made on histologic grounds alone when the history indicates a solitary lesion.