Characteristics of the structural components of pilosebaceous follicles in the differential diagnosis of non-cicatricial alopecia

BACKGROUND: Research into the pathogenesis of non-cicatricial alopecia involves investigating the mechanisms behind disruptions in the biological rhythm of hair growth and assessing the anagen-to-telogen hair ratio, without considering changes in pilosebaceous follicle morphology and its structural components. The functional role of the pilosebaceous follicle’s structural components (the hair follicle, outer root sheath, and inner root sheath) is not fully understood. There is no reliable evidence of correlations between changes in the hair follicle, the external and internal root sheaths, and the development of a specific type of alopecia.

AIM: This study aimed to investigate changes in structural components of the pilosebaceous follicle associated with non-cicatricial alopecia.

METHODS: Histological and morphometric examinations were conducted for scalp biopsy samples obtained from 191 patients with non-cicatricial alopecia and 20 control patients.

RESULTS: An assessment of pilosebaceous follicle thickness in the subcutaneous fat tissue of the scalp in patients with various types of non-cicatricial alopecia revealed that hair follicles were thinner than those in the control group. The most significant changes were observed in patients with alopecia areata. A decreased thickness of the external root sheath was found in all hair loss groups, with the lowest values observed in alopecia areata and telogen effluvium. The internal root sheath was thinner in cases of diffuse telogen effluvium and alopecia areata but not in androgenetic alopecia.

CONCLUSION: In patients without hair loss, the most significant changes in the thickness of the hair follicle and the outer and inner root sheaths occurred at the transition from the reticular dermis to the sebaceous gland. In patients with alopecia, however, thinning of these structural components began in the subcutaneous fat tissue.