The histopathology of noncicatricial alopecia.

During the past 2 decades, the use of transverse sections in the evaluation of scalp biopsy specimens has led to a better understanding of the histopathologic changes in both cicatricial and noncicatricial alopecia. However, the technique has provided the most significant gains in the study of the latter type of alopecia, where evaluation of follicle density and follicular dynamics are integral to accurate diagnosis. This report reviews the histopathologic findings of four common types of noncicatricial alopecia: androgenetic alopecia, telogen effluvium, alopecia areata, and trichotillomania/chronic traction alopecia.