[How I explore ... primary cicatricial alopecias].

Primary cicatricial alopecias (PCA) result from the inflammatory destruction of the hair follicle, followed by its replacement by a fibrotic streamer. The involvement of multipotent stem cells of the hair follicle is possible through a transdifferentiation pathway. The diagnosis relies on clinico-pathologic correlations. PCA are classified as the neutrophilic, lymphocytic and mixed types. Each of these groups gather specific disorders including folliculitis decalvans, dissecting folliculitis of the scalp, erosive pustulosis of the scalp, keloidal acne of the nape, frontal fibrosing alopecia, lichen planopilaris and lupus erythematosus.