[Rare or unusual forms of psoriasis].

Apart from plaque-type psoriasis, there are multiple particular or rare clinical presentations, according to signs and symptoms, localization or distribution of lesions. Psoriasis can affect mucous membranes, especially the genital areas of male and female patients, causing pain or burning sensation and decreased quality of life. Geographic tongue is not specific of psoriasis, but is more frequent in this context. Other localizations like the lips and the eylids are rare, but should not be overlooked. Certain lesions have an unusual distribution, like psoriasis gyrata and blaschko linear forms. Pustules are frequently observed on the palms and soles. Acrodermatitis continua is a rare chronic pustular condition affecting the acral areas, mainly the fingers, which is associated with severe nail involvement. Nails can also be involved in the unusual pachydermo-periostitis, a clinical form of psoriasis without epidermal lesions, which has characteristic radiologic presentation.