title: Histopathologic features of alopecia areata incognito: a review of 46 cases.
abstract: BACKGROUND
  Alopecia areata (AA) incognito represents a variant of AA characterized by acute diffuse hair thinning. Dermoscopy shows yellow dots and short regrowing hairs. The differential diagnosis with telogen effluvium (TE) and androgenetic alopecia may be difficult.
  
  
  METHODS
  In order to establish histopathological criteria for the diagnosis of AA incognito, we evaluated retrospectively 92 specimens (46 horizontal and 46 vertical) of 46 patients diagnosed with AA incognito within 1 year. All specimens were assessed for 20 features, including hair counts and follicular ratios. The numbers were compared with 46 control specimens, consisting of 21 cases of TE and 25 cases of androgenetic alopecia.
  
  
  RESULTS
  The following main criteria are proposed: (a) preserved number of follicular units and decreased number of terminal follicles; (b) increased number of telogen structures (mean count of 37%) with presence of at least one telogen germinal unit or/and one small telogen follicle (c) decreased terminal:vellus ratio (mean ratio of 3.3 : 1) and (d) dilated infundibular openings.
  
  
  CONCLUSIONS
  Two histopathologic clues for AA incognito include the presence of dilated infundibular openings and small basaloid aggregates of cells with round, irregular or polygonal shape, lack of hair shaft and no apoptosis in the outer root sheath, corresponding to small telogen follicles.
authors.affiliation: Department of Dermatology and Cutaneous Surgery, Miller School of Medicine, University of Miami, 1600 NW 10th Avenue, Miami, FL 33136, USA. mmiteva@med.miami.edu
authors.forename: Mariya
authors.initials: M
authors.lastname: Miteva
authors.forename: Cosimo
authors.initials: C
authors.lastname: Misciali
authors.forename: Piero A
authors.initials: PA
authors.lastname: Fanti
authors.forename: Antonella
authors.initials: A
authors.lastname: Tosti
mesh_terms: D000328:Adult; D000506:Alopecia Areata / Q000473:pathology*; D005260:Female; D018859:Hair Follicle / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012867:Skin / Q000473:pathology*