Background: Premature desquamation of the inner root sheath (IRS) is an important histological marker for central, centrifugal, cicatricial alopecia (CCCA), and an inherently defective IRS may be responsible. Cytokeratin 75 (K75; formerly K6hf) is an appealing candidate for study because K75 is specifically expressed in the companion layer of the hair follicle, the interface for IRS desquamation. Also, K75 abnormalities have been found in other hair diseases bearing similarities to CCCA.
Methods: We used a commercially available antibody to K75 on formalin-fixed, paraffin-embedded tissue from clinically and histologically "normal" scalp (n=9); clinically diseased scalp from patients with CCCA (n=15); and clinically "normal" scalp from patients with CCCA (n=6).
Results: K75 expression disappears during the process of IRS desquamation, and loss of expression begins even when IRS desquamation is in its incipient phase. Also, K75 has a characteristic pattern of expression in telogen follicles.
Conclusions: K75 expression is closely associated with the process of desquamation of the IRS. This process occurs prematurely (below the isthmus) in many follicles from patients with, but not without, CCCA. K75 expression highlights premature desquamation of the IRS in CCCA, but may not be directly involved in disease pathogenesis.