title: Absence of catagen/telogen phase and loss of cytokeratin 15 expression in hair follicles in lichen planopilaris.
abstract: BACKGROUND
  Lichen planopilaris (LPP) is a lymphocyte-mediated cicatricial alopecia mostly involving the bulge region of the hair follicle. The origin of LPP is unknown. Therapy for LPP often does not prevent disease progression. We describe histologic and immunohistologic features that aid in diagnosis and provide an explanation for disease progression in LPP.
  
  
  OBJECTIVE
  We sought to demonstrate a decrease in the number of catagen-/telogen-phase follicles and to confirm the loss of cytokeratin 15 (CK15) expression in the stem cells of LPP-affected follicles.
  
  
  METHODS
  In all, 144 LPP cases were retrieved; 55 cases were stained immunohistochemically, targeting the CK15 antigen with 40 cases ultimately analyzed for CK15 expression.
  
  
  RESULTS
  Catagen/telogen phase was significantly decreased or absent in all cases of LPP, a novel clue useful in histologic diagnostics. The loss of CK15+ stem cells in most affected follicles in LPP was also confirmed, with unaffected follicles retaining CK15+ stem cells.
  
  
  CONCLUSIONS
  Limited tissue for analysis remained in the clinical sample tissue blocks.
  
  
  CONCLUSIONS
  Damaged follicles that have lost their CK15+ stem cells disappear when they enter catagen phase. CK15+ stem cell loss explains the clinical observation that LPP progresses despite immunosuppressive therapies. Finally, the absence of catagen/telogen hair follicles is a helpful diagnostic clue for LPP.
authors.affiliation: Department of Pathology, Oregon Health and Science University, Portland, Oregon.
authors.forename: Arlette
authors.initials: A
authors.lastname: Habashi-Daniel
authors.affiliation: Department of Dermatology, Oregon Health and Science University, Portland, Oregon.
authors.forename: Janet L
authors.initials: JL
authors.lastname: Roberts
authors.affiliation: Northwest Dermatology and Research Center LLC, Portland, Oregon.
authors.forename: Nisha
authors.initials: N
authors.lastname: Desai
authors.affiliation: Department of Pathology, Oregon Health and Science University, Portland, Oregon; Department of Dermatology, Oregon Health and Science University, Portland, Oregon; Department of Biomedical Engineering, Oregon Health and Science University, Portland, Oregon. Electronic address: cthompson@cta-lab.com.
authors.forename: Curtis T
authors.initials: CT
authors.lastname: Thompson
mesh_terms: D006197:Hair / Q000254:growth & development; D018859:Hair Follicle / Q000378:metabolism / Q000503:physiopathology*; D006801:Humans; D053569:Keratin-15 / Q000378:metabolism*; D008010:Lichen Planus / Q000473:pathology / Q000503:physiopathology*; D013234:Stem Cells / Q000378:metabolism* / Q000502:physiology
chemical_list: D053569:Keratin-15
keywords: anagen; bulge; catagen; cytokeratin 15; follicular cycle; follicular stem cell; immunohistochemistry; infundibulo-isthmic; lichen planopilaris; telogen