Solitary lichenoid benign keratosis: a clinicopathological investigation and comparison to lichen planus.

The dermatopathologist is sometimes confronted with a single lesion biopsy showing the histopathology of a lichen planus (LP) taken from a patient having no further clinical signs of LP. This entity represents the 'solitary lichenoid benign keratosis' (SLBK). We report about 202 patients with 204 SLBK lesions which were diagnosed between 1981 and 1987. The mean age of these patients was 59 years, 62.4% were females. Only 2 of the 202 patients showed multiple lesions. In 30.6% the SLBK was located in the face and neck area. In the order of frequency the following clinical diagnoses were made: basal cell carcinoma, senile keratosis, Bowen's disease or seborrheic wart among others. We were able to distinguish three clinical types: (1) an erythematous type, (2) a papulokeratotic type and (3) a plaque-like type. The histopathological difference between SLBK and LP is primarily quantitative. The SLBK shows the following pronounced criteria: parakeratosis, vacuolized keratinocytes in the basal layer, a spongiotic epidermis in the center of the lesion with exocytosis of lymphoid cells, edema in the papillary layer, elastosis and plasma cells. Regularly one can find 'lentigo-senilis'-like lesions at the edge of an SLBK. Immunohistopathology showed no characteristic features in SLBK. The pathogenesis of this distinct entity is not yet clear.