New Histopathologic Findings in Scarring Alopecias: The Role of Adipose Tissue and Eccrine Sweat Coils in Frontal Fibrosing Alopecia, Fibrosing Alopecia in a Pattern Distribution, and Lichen Planopilaris.

Context.—: Clinical, dermoscopic, and histologic diagnostic criteria may overlap in cases with scarring and nonscarring alopecia, making diagnosis difficult for clinicians and pathologists. New histopathologic discoveries indicate that the cutaneous adnexal structural and homeostatic unit made up of the pilosebaceous unit, eccrine sweat gland coils (ESGCs), and dermal white adipose tissue may have a role in hair follicle renewal.
Objective.—: To verify the presence of adipose tissue in the dermis at the level of the isthmus, infiltrating the bundles of the arrector pili muscle in biopsies from the scalp of 3 scarring alopecias: frontal fibrosing alopecia (FFA), fibrosing alopecia in a pattern distribution (FAPD), and lichen planopilaris (LPP).
Design.—: We performed a retrospective and descriptive survey of 71 female scalp biopsies from 2016 to 2022 diagnosed at the Dermatopathology Laboratory at Fluminense Federal University of Rio de Janeiro. Two pathologists reviewed and diagnosed the cases, correlating pathologic features with clinical and dermoscopic findings.
Results.—: The histopathologic findings of adipose tissue infiltration in the dermis at the level of the isthmus and in the bundles of the arrector pili muscle and the displacement of ESGCs were more frequently identified in FFA, followed by FAPD and less frequently found in LPP.
Conclusions.—: According to our research, adipose tissue infiltration in the dermis at the level of the isthmus and in the bundles of the arrector pili muscle and the displacement of ESGCs were observed in 3 scarring alopecias (FFA, FAPD, and LPP) and seems to be involved in the development of scarring alopecia.
Competing Interests: The authors have no relevant financial interest in the products or companies described in this article.
(© 2024 College of American Pathologists.)