Investigation of the hair follicle inner root sheath in scarring and non‐scarring alopecia

BACKGROUND: Premature desquamation of the inner root sheath (IRS) is described as a defining histologic feature of follicular degeneration syndrome/central centrifugal cicatricial alopecia (CCCA). However, IRS abnormalities have been noted in other types of alopecia. DESIGN: We evaluated the IRS in terminal hair follicles with transverse sections stained with hematoxylin-eosin and Ziehl-Neelsen stains in 22 non-scarring (7 areata and 15 androgenetic) and 21 scarring (13 CCCA, 2 lichen planopilaris, 2 lupus erythematosus, 1 folliculitis decalvans and 3 end stage) alopecia cases. In addition, we evaluated 15 normal controls with longitudinal sections to establish the level of IRS desquamation. RESULTS: The IRS was present in 99.5 +/- 0.01% (mean +/- standard error) of normal follicles at the level of the arrector pili muscle/sebaceous gland/sweat gland coil (L2) and variably present at higher levels. The IRS was present at L2 in 97.9 +/- 1.5% of alopecia areata, 87.4 +/- 5.3% of androgenetic alopecia, 59.3 +/- 7.0% of CCCA and 49.4 +/- 11.3% of other scarring alopecia follicles. CONCLUSIONS: Premature desquamation of the IRS was identified in CCCA; however, it was also noted in other scarring alopecia cases. IRS premature desquamation is a non-specific histologic feature in scarring alopecia and cannot be used alone as a defining feature of CCCA.