Lichen planus: an ultrastructural study.

Ultrastructural features of skin lesions are described in 11 patients with lichen planus. Keratinocytes and melanocytes in the basal layer show loss of nuclear membrane, disappearance of nucleoli, homogenization of nuclear material, and aggregation of tonofilaments around the nucleus to resemble cells in the late prophase of the mitotic cycle except that there is no clumping of chromosomes. These cells undergo fibrillar transformation to form densely packed fibrillar bodies (colloid bodies) which are the size and shape of normal cells and frequently have cytoplasmic organelles. Ten per cent of the mainly lympho-histiocytic cells in the dermal infiltrate show changes such as multiple cell membrane discontinuities, disintegration of cytoplasm, and breaks in the nuclear membrane with spilling of nuclear substance either into the cytoplasm or the extracellular space. The shape, size and occasional fibrillar changes in the nuclei and cytoplasm of these cells resemble colloid bodies. Contact sites frequently occurred between cells in the dermal infiltrate, especially between lymphocytes and macrophages. It appears that primary injury to the basal layer cells occurs during the early phase of the mitotic cycle and antigen from this primary site may evoke a cell-mediated type of hypersensitivity reaction. Colloid bodies evolve from cells which have injured nuclei and undergo fibrillar transformation. Dermal as well as epidermal cells may contribute to colloid body formation.