Histopathologic diagnosis of alopecia: clues and pitfalls in the follicular microcosmos

In recent years the increased number of scalp biopsies in alopecia has afforded the dermatopathologist improved confidence in distinguishing the histopathologic characteristics of ‘classic’ scarring and non-scarring alopecias, as well as the spectrum of their presentation. Occasionally, however, histopathologic ‘dogmas’ have been disproven. The loss of sebaceous glands considered to be a clue to scarring alopecia or the peribulbar lymphoid cell infiltrate diagnostic of alopecia areata may present in unconventional scenarios, and thus, represent pitfalls. Clues to diagnose histopathologically ‘silent’ (invisible) alopecias, the identification of multiple etiologies, and awareness of the ‘time-factor’ are herein discussed.