Histopathology of alopecia: a clinicopathological approach to diagnosis.

Interpretation of the histopathological findings of primary scarring and non-scarring alopecias may prove daunting. This is especially true if the biopsy specimen is inadequate, and the clinical history and pattern of the alopecia are not known. Common forms of scarring alopecias discussed here are the lymphocytic (discoid lupus erythematosus, lichen planopilaris, central centrifugal cicatricial alopecia, pseudopelade of Brocq), the neutrophilic (folliculitis decalvans, dissecting folliculitis), and the mixed (acne keloidalis) entities. The non-scarring alopecias reviewed are androgenic alopecia, telogen effluvium, alopecia areata, trichotillomania and traction alopecia. In all cases of primary alopecia, adequate tissue sampling and appropriate laboratory processing, in combination with pertinent clinical information, provide the key to diagnosis.