[Lichen planus, a T-lymphocyte mediated reaction involving the skin and mucous membranes].

Lichen planus concerns a benign skin disorder without involvement of other organ systems. Its course is generally limited to less than a year. Classic lichen planus is characterized by pruritic, violaceous, plane papules which occur most commonly on the inside of the wrists, the lower back, the lower legs and the perimalleolar region of adults aged between 30-60 years. Frequently, oral and genital mucous membrane lesions are involved. Erosive mucosal lesions are particularly painful and long-lasting. Many clinical variants have been described ranging from lichenoid drug eruptions to associations with graft-versus-host disease. The cause of lichen planus is unknown. An immunopathological pathogenesis with T-lymphocytes directed against basal keratinocytes or the basal membrane zone is assumed. Multiple therapeutic options exist: local and systemic corticosteroids, psoralens with ultraviolet A light (PUVA), retinoids, cyclosporin.