Histopathologic Evaluation of Alopecias

The document from 2006 provides a comprehensive review of the histopathologic evaluation of alopecias, emphasizing the importance of clinicopathologic correlation for accurate diagnosis due to the overlap in histopathologic features among different types of alopecia. It describes the hair growth cycle, with anagen being the most affected phase by alopecia, and discusses the ambiguity in classifying alopecias as scarring or nonscarring, noting the prognostic importance of identifying true scarring. Elastic tissue stains are highlighted as useful in differentiating these alopecias. Androgenetic alopecia, the most common form of hair loss, is characterized by follicle miniaturization and a decreased anagen:telogen ratio, with the significance of perifollicular inflammation remaining unclear. The document also covers telogen effluvium, chronic telogen effluvium, alopecia areata, trichotillomania, and traction alopecia, detailing their histopathologic features and the necessity of histopathology for differential diagnosis. Additionally, it discusses the classification and pathogenesis of primary scarring alopecias, including stem cell failure, sebaceous gland damage, and destruction of the outer root sheath. The document further examines the differentiation between DLE, lichen planopilaris, and classic pseudopelade of Brocq, highlighting the role of special stains and immunofluorescence. Lastly, it touches on mixed inflammatory primary scarring alopecias, such as folliculitis keloidalis, and the importance of histopathologic differential diagnosis.