title: Benign keratosis with a spectrum of follicular differentiation: a case series and investigation of a potential role of human papilloma virus.
abstract: BACKGROUND
  A variety of dermatopathologic entities are histologically defined by the presence of follicular differentiation. Follicular differentiation confined to the epidermis may follow induction from dermal mesenchymal proliferations, as in a nevus sebaceus of Jadassohn, or represent endogenous proliferations such as the tumor of the follicular infundibulum or trichilemmoma.
  
  
  METHODS
  We report on five cases of a histologically distinct form of benign keratosis showing variable follicular differentiation. Clinicopathologic correlation and analysis of a potential human papilloma virus pathogenesis was investigated.
  
  
  RESULTS
  Each of the cases arose on the trunk or extremities of three men and two women with a mean age at presentation of 66.6 years. All of the lesions showed variable follicular differentiation, with germinative basaloid cells, matrical cells with matrical keratinization, inner root sheath with trichohyalin granules, or glycogenated lower outer root sheath. Immunohistochemical staining for human papilloma virus was negative in each case.
  
  
  CONCLUSIONS
  There exists a distinct entity, histologically defined as a keratosis with variable follicular differentiation, which has not been previously described. These lesions do not appear to be pathogenically related to human papilloma virus infection.
authors.affiliation: Department of Dermatology, MetroHealth Medical Center Campus of Case Western Reserve University School of Medicine, Cleveland, Ohio 44109, USA.
authors.forename: S
authors.initials: S
authors.lastname: Somach
authors.forename: M
authors.initials: M
authors.lastname: Morgan
mesh_terms: D000368:Aged; D002454:Cell Differentiation; D005260:Female; D018859:Hair Follicle / Q000473:pathology / Q000821:virology; D006801:Humans; D017492:Keratosis, Seborrheic / Q000473:pathology* / Q000821:virology*; D008297:Male; D008875:Middle Aged; D027383:Papillomaviridae; D030361:Papillomavirus Infections / Q000473:pathology*; D014412:Tumor Virus Infections / Q000473:pathology*