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LICHEN PLANUS AND LICHEN PLANUS‐LIKE ERUPTIONS: PATHOGENESIS AND ASSOCIATED DISEASES

Lichen planus (LP) is a clearly defined papulosquamous disease characterized by typical cutaneous and mucosal lesions. The term "lichen" was derived from a group of plants to which LP lesions bear some resemblance. The term "lichenoid" describes LP-like eruptions, which may be associated with certain diseases or may be induced by various drugs. The pathogenesis of lichen planus and LP-like eruptions is not well understood. An abnormal immune response is considered to be the basic underlying mechanism. Histologic and immunofluorescence studies, as well as recent data based on monoclonal antibody techniques and human leukocyte antigen (HLA) typing, support this hypothesis. Additional support comes from the association between LP and certain systemic disorders.