title: Occult neurofibroma and increased S100 protein in the skin of patients with neurofibromatosis type 1: new insight to the etiopathomechanism of neurofibromas.
abstract: BACKGROUND
  Neurofibromas represent proliferation of the connective tissue cells of peripheral nerves and deposition of collagenous extracellular matrix. There is evidence that the appearance and growth of neurofibromas may be associated with prior or ongoing mechanical trauma in patients with neurofibromatosis type 1 (NF1).
  
  
  OBJECTIVE
  To study the histologic characteristics of apparently healthy skin of patients with NF1.
  
  
  METHODS
  The histologic features of healthy-looking skin of patients with NF1 were analyzed.
  
  
  METHODS
  University hospital.
  
  
  METHODS
  Ten patients who fulfilled the criteria for NF1.
  
  
  METHODS
  Punch biopsy specimens of healthy-looking skin of the forearm from 9 volunteer patients and of the upper eyelid during cosmetic operation from 1 volunteer patient were obtained.
  
  
  METHODS
  The main outcomes were not predicted, and the hypothesis was formulated during data collection.
  
  
  RESULTS
  Apparently unaffected skin of 5 patients with NF1 was studied by routine histologic testing with respect to expression of S100 protein. Unexpectedly, analysis of the samples revealed the presence of a small neurofibroma tumor in one of the samples. The tumor was located in deep dermis around a hair follicle. In addition, neurofibromatous tissue not large enough to be called a tumor was found on the same anatomical location in another patient. In further studies, 10 punch biopsy specimens of apparently healthy skin from patients with NF1 were similarly sectioned and analyzed. No tumors were found in these additional samples. In 4 patients, however, abundant S100 protein-positive cells were located within collagenous extracellular matrix surrounding hair follicles.
  
  
  CONCLUSIONS
  The skin of patients with NF1 might be more widely affected than previously thought and occult neurofibromas are not rare.
authors.affiliation: Department of Dermatology, University Hospital of Oulu, FIN-90220 Oulu, Finland. seija-liisa.karvonen@oulu.fi
authors.forename: S L
authors.initials: SL
authors.lastname: Karvonen
authors.forename: M
authors.initials: M
authors.lastname: Kallioinen
authors.forename: H
authors.initials: H
authors.lastname: Ylä-Outinen
authors.forename: M
authors.initials: M
authors.lastname: Pöyhönen
authors.forename: A
authors.initials: A
authors.lastname: Oikarinen
authors.forename: J
authors.initials: J
authors.lastname: Peltonen
mesh_terms: D005142:Eyelid Neoplasms / Q000473:pathology; D005542:Forearm; D006801:Humans; D009382:Neoplasms, Unknown Primary / Q000209:etiology / Q000473:pathology*; D009455:Neurofibroma / Q000209:etiology / Q000473:pathology*; D009456:Neurofibromatosis 1 / Q000378:metabolism* / Q000473:pathology*; D009418:S100 Proteins / Q000378:metabolism*; D012878:Skin Neoplasms / Q000209:etiology / Q000473:pathology*
chemical_list: D009418:S100 Proteins