Premature Desquamation of the Inner Root Sheath in Noninflamed Hair Follicles as a Specific Marker for Central Centrifugal Cicatricial Alopecia

Background: Premature desquamation of the inner root sheath (PDIRS) is considered one of the distinctive features in central centrifugal cicatricial alopecia (CCCA). However, PDIRS can be seen in other alopecia subtypes, and its utility in the diagnosis of CCCA has been debated. We aimed to examine a large cohort of alopecia cases for the presence of PDIRS in association with and without inflammation to determine whether PDIRS in noninflamed follicles can be used as a specific marker of CCCA. Methods: Retrospective analysis was performed on 501 histologically unambiguous cases of alopecia (111 of CCCA, 102 of lichen planopilaris, 62 of discoid lupus erythematosus, 16 of acne keloidalis nuchae, 27 of folliculitis decalvans, 80 of androgenetic alopecia, 97 of alopecia areata, and 6 of psoriatic alopecia). The frequency of PDIRS, including cases with and without inflammation, was determined. Results: PDIRS was identified in all alopecia subtypes evaluated. When PDIRS was identified in lichen planopilaris, discoid lupus erythematosus, acne keloidalis nuchae, and alopecia areata, 100% of cases were in inflamed follicles. PDIRS in noninflamed follicles occurred in 73% (81/111) of CCCA, 33% (2/6) of psoriatic alopecia, 11% (3/27) of folliculitis decalvans, and 1% (1/97) of androgenetic alopecia. The presence of PDIRS in at least one noninflamed hair follicle correlated with a diagnosis of CCCA with a sensitivity of 73% and a specificity of 98% (P-value <0.0001). Conclusion: Identifying PDIRS in noninflamed hair follicles is a useful histologic feature in the evaluation of scalp biopsies and seems to be relatively specific for CCCA.