Histologic Features of Alopecias–Part I: Nonscarring Alopecias

The document from 2015 reviews the histological features of various nonscarring alopecias, which are hair loss conditions where the hair follicles remain intact and can potentially regrow hair. It highlights the importance of understanding the hair cycle and the morphological changes in hair follicles, as alopecias often affect specific phases, especially the anagen phase. The review details key histopathological features for diagnosing different nonscarring alopecias, such as androgenic alopecia, characterized by follicle miniaturization and debated inflammatory infiltrate, and telogen effluvium, marked by a high number of telogen phase follicles. Chronic telogen effluvium, alopecia areata, syphilitic alopecia, trichotillomania, and traction alopecia are also discussed, each with distinct histological features that aid in diagnosis. Traction alopecia, in particular, is characterized by a decrease in terminal hair follicles without inflammatory infiltrate, and can progress to an irreversible stage with fibrosis. The document underscores the necessity of correlating clinical and pathological findings for accurate diagnosis and understanding the progression of these conditions.