[Anal manifestations of lichen planus].

Lichen planus (LP) is an entity endowed with a striking polimorphysm and with a diversity of topographic localizations. In spite of the diagnostic difficulties that the combination of these factors occasionally produce, the histopathology of the lesion is tipical and diagnostic. Our presentation seems to be justified since, to the best of our knowledge, the anal localization of the disease has not been reported and it is also rare. The finding of these anal manifestation has not been casual. With the certitude that there was no reason why LP could not appear in a semimucosa so much alike that of the lips we have systematically examined the anal region of patients bearing lesions of LP elsewhere. Anal lesions that appeared to correspond to LP were detected and their histopathology confirmed the existence of LP in some of these cases. The structural changes permit the grouping of cases in four categories: Tipical LP of the anal semimucosa. LP of the anal semimucosa masked by coexistent lichen simplex chronicus (neurodermatitis). Serial sections of the paraffin block or biopsy of a nearby area usually prove diagnostic. Neurodermatitis associated to a lichenoid tissue reaction: Focal effacement of the basal membrane associated to lymphoid infiltrate of the upper dermis. Neurodermatitis without lichenoid features. It is our interpretation that this localization of LP may be due to a Köbner's phenomenon provoked by scratching induced by pruritus, as it occurred in our cases, or by other microtraumas so common to the area.(ABSTRACT TRUNCATED AT 250 WORDS)