ABSTRACT
This chapter describes the more important diseases of each group, and analyzes their typical trichoscopic features. The course of the disease includes gradual miniaturization of the hair follicles, gradual shortening of the anagen phase and prolongation of the post-exogen part of the telogen phase. The process is driven by dihydrotestosterone that locally interferes with the hair follicle, while the level of circulating androgens is usually in normal range. Alopecia areata (AA) belongs to the group of nonscarring alopecias and it is a lymphocyte-driven autoimmune hair disorder. The clues for trichoscopic diagnosis of AA include “exclamation mark” hairs, tapered hairs, and Pohl-Pinkus constrictions of the hair shafts, broken hairs, vellus hairs, and circle hairs. ”Exclamation mark” hairs represent an almost pathognomonic trichoscopic feature of AA. They are fractured hairs with thick hyperpigmented distal ends and thin, hypopigmented proximal ends, which are responsible for the characteristic morphology.
