Lichen planus: review and update on pathogenesis

Lichen planus (LP) is a common oral disorder which may represent the manifestation of a mucosal reaction to a variety of aetiological factors. Of the many immunological changes described in LP several may be epiphenomena although a cell-mediated immune response to unidentified antigens or antigenic changes clearly is involved. Associations with drugs or systemic disorders are well-defined in some patients but may, in others, be aleatoric. Finally, the prognosis of oral LP not only differs from that of cutaneous LP but there is little doubt that in a few instances LP is a premalignant condition.

Epithelial differentiation patterns in buccal mucosa affected by lichen planus

The epithelium derived from buccal mucosa affected by lichen planus reticularis was subjected to histometric and stereologic analysis. Point counting procedures were employed to analyse a total of 2,220 electron micrographs sampled from 5 epithelial strata in 9 biopsies, 7 with distinct and 2 with faint Wickham's striae. Histologically the reticular elements presented an atrophy of the entire epithelium which had altered its differentiation pattern from that of normal buccal epithelium. The epithelium of faintly striated lichen planus differed from that of distinctly striated lichens in regard to a series of cytoplasmic organelles representing key features of stratified epithelia, i.e. the volume densities of glycogen, membrane coating granules, keratohyalin granules, cytoplasmic filaments and the cytoplasmic ground substance. The data emphasize that the clinically discernable features of reticular lichen planus of the buccal mucosa are produced by at least two different stages in the deviation of the epithelial differentiation pattern from normality, one stage (distinct striae) being more drastically altered than the other (faint straie).

The inflammatory infiltrate in lichen planus lesions. An autoradiographic and ultrastructural study

The labeling index of the infiltrate of oral lichen planus lesions was significantly greater than that of normal mucosa, and its labeling activity redistributed, as determined by in vitro autoradiography. An electron microscopic examination of the infiltrate of lichen planus lesions of oral mucosa and skin supported the concept that the lichen planus infiltrate represents a cell mediated immune response in which T lymphocytes and macrophages are predominant.