title: Epidermal psoriasiform hyperplasia, an unrecognized sign of folliculitis decalvans: A histological study of 26 patients.
abstract: BACKGROUND
  Follicular hyperkeratosis along with hyperplasia of the follicular and interfollicular epithelia are major histopathological characteristics of hidradenitis suppurativa (HS). The presence of an occasional thickening of lesional skin in some folliculitis decalvans (FD) patients and histological similarities between FD and HS led us to look for epidermal hyperplasia and follicular hyperkeratosis in FD patients.
  
  
  METHODS
  We performed a retrospective histological analysis of 26 patients with FD.
  
  
  OBJECTIVE
  We sought to find out whether the presence of hyperplasia of the interfollicular epidermis and of the follicular epithelia could be verified in FD, with reference to the work of von Laffert et al. concerning HS.
  
  
  RESULTS
  The main quantitative and qualitative data were: follicular hyperkeratosis (77%), hyperplasia of the interfollicular epidermis (92%) with a psoriasiform aspect (88%), atrophy of the follicular epithelia (85%), plasma cells in infiltrate (92%) in large quantities (42%), follicular microcysts (60%), atrophy of the sebaceous glands (85%) and polytrichia (54%).
  
  
  CONCLUSIONS
  Epidermal hyperplasia, sometimes psoriasiform and follicular microcysts, are significant histological signs of FD, which have been ignored until now although they seem very common.
authors.affiliation: Hôpital Saint-Louis, Centre Sabouraud, Paris, France.
authors.forename: Bruno
authors.identifier: http://orcid.org/0000-0001-7137-8527
authors.initials: B
authors.lastname: Matard
authors.affiliation: Department of Dermatopathology, Policlinique Hôpital Saint Louis, Paris, France.
authors.forename: Benedicte
authors.initials: B
authors.lastname: Cavelier-Balloy
authors.affiliation: Hôpital Saint-Louis, Centre Sabouraud, Paris, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Reygagne
mesh_terms: D004817:Epidermis / Q000378:metabolism / Q000473:pathology; D005260:Female; D005499:Folliculitis / Q000378:metabolism / Q000473:pathology; D006801:Humans; D006965:Hyperplasia; D008297:Male; D010950:Plasma Cells / Q000378:metabolism / Q000473:pathology; D012627:Sebaceous Glands / Q000378:metabolism / Q000473:pathology
keywords: dysbiosis; epidermal hyperplasia; follicular microbiota; folliculitis decalvans; hidradenitis suppurativa