ABSTRACT
Androgenetic alopecia (AGA) is an androgen-related hair disorder characterized by gradual and progressive, irreversible follicular miniaturization resulting in patterned (men and women) or diffuse (women) thinning in genetically predisposed individuals.
This is the most common type of hair biopsy in the daily practice. Most biopsies are obtained from women.
Men with classic AGA are rarely biopsied and a biopsy is usually done to exclude focal lichen planopilaris (LPP)/fibrosing alopecia in a pattern distribution (FAPD) (see also Chapter 7), especially prior to hair transplant surgery.
Trichoscopy is very helpful for the diagnosis of AGA, which is based on detecting hair shaft variability. In women and men, usually 6 sites are studied in the parietal scalp. Two sites in the bitemporal scalp and one in the uninvolved occipital scalp can be added in men (for comparison) (Figure 11.1). Posterior scalp (outside the patterned area) should be studied on trichoscopy for comparison. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig11_1.tif"/>
Main trichoscopic features include:
Hair shaft variability (unisotrichosis): hair shafts of different thickness (thick, intermediate and vellus) with increased proportion of the vellus hairs (Figure 11.2) There is clear hair shaft variability in this case of AGA (×40). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig11_2.tif"/>
Decreased number of hairs per follicular unit and increased number of single hairs (Figure 11.3) Most follicular units contain single hairs. Note the irregular pigmented network due to sun-induced hyperpigmentation of the scalp (×20). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig11_3.tif"/>
Yellow dots (irregular distributed and mainly in frontal scalp) (Figure 11.4) Yellow dots in frontal scalp in androgenetic alopecia (×40). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig11_4.tif"/>
Peripilar sign (about 1 mm perifollicular brown halo corresponding to mild infundibular lymphocytic infiltrate and fine fibroplasia), which can be white in Fitzpatrick skin type IV-VI (Figure 11.5)
