Lichen nitidus: a histologic and electron microscopic study.

A lesion of lichen nitidus in a 53-year-old man was examined by histology and electron microscopy. The histology showed typical features. The electron microscopy revealed primary changes in hydropic degeneration of basal cells which possibly indicated severe edema between the basal keratinocytes and in the subepidermal area. The basal keratinocytes themselves were not particularly altered, except for clustered micro-vacuolar structures in a small portion of the peripheral cytoplasm. In one of the eight blocks observed, the cytoplasmic process of a mast cell was found between the basal keratinocytes, indicating that mast cells may possibly infiltrate the epidermis in lichen nitidus. Scattered mast cells in the dermis were also noted. Thus primary pathologic changes of lichen nitidus may be induced by severe edema, which was accompanied by inflammatory cells including mast cells, in the region of the dermal-epidermal junction.