title: Skin responses to fractional photothermolysis.
abstract: OBJECTIVE
  Fractional photothermolysis (FP) is a new concept using arrays of microscopic thermal damage patterns to stimulate a therapeutic response. We analyzed epidermal and dermal response to FP with the aim of correlating histological and clinical response.
  
  
  METHODS
  Twelve subjects received a single treatment with a prototype diode laser emitting at a wavelength of 1,500 nm, delivering 5 mJ per microscopic treatment zone (MTZ), and a density of 1,600 MTZs/cm(2) on the forearm. Biopsies were procured over a period of 3 months. The biopsies were analyzed by two blinded dermatopathologists using hematoxylin and eosin (Hematoxylin and Eosin Stain), Elastica von Gieson, nitro-blue-tetrazolium-chloride (NBTC) viability, and immunohistochemistry stains. Furthermore, the treatment sites were evaluated in vivo by confocal microscopy.
  
  
  CONCLUSIONS
  Twenty-four hours after fractional photothermolysis, the continuity of the epidermal basal cell layer is restored. Complete epidermal regeneration is obtained 7 days after the treatment. Microscopic epidermal necrotic debris (MENDs) are seen as early as 1 day after FP. MENDs contain melanin pigment, and are shed from the epidermis within 7 days. Evidence of increased collagen III production is shown with immunohistochemistry (IHC) staining 7 days after FP. IHC for heat shock protein 70 (HSP 70) shows the expression of HSP 1 day after FP, and IHC for alpha smooth muscle actin shows the presence of myofibroblasts 7 days after FP. These findings are concordant with the induction of a wound healing response by FP. There is no evidence of residual dermal fibrosis 3 months after treatment.
  
  
  CONCLUSIONS
  A single treatment with fractional photothermolysis induces a wound healing response in the dermis. A mechanism for the precise removal of epidermal melanin is described, in which MENDs act as a melanin shuttle.
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, 02114, USA. h.laubach@partners.org
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Laubach
authors.forename: Zeina
authors.initials: Z
authors.lastname: Tannous
authors.forename: R Rox
authors.initials: RR
authors.lastname: Anderson
authors.forename: Dieter
authors.initials: D
authors.lastname: Manstein
mesh_terms: D000199:Actins / Q000378:metabolism; D000328:Adult; D001706:Biopsy; D024061:Collagen Type III / Q000096:biosynthesis; D020405:Dermis / Q000473:pathology / Q000528:radiation effects*; D004817:Epidermis / Q000473:pathology / Q000502:physiology / Q000528:radiation effects*; D005347:Fibroblasts / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D053685:Laser Therapy / Q000379:methods*; D018613:Microscopy, Confocal; D008875:Middle Aged; D032389:Myocytes, Smooth Muscle / Q000378:metabolism; D009336:Necrosis; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D012038:Regeneration; D013997:Time Factors; D014945:Wound Healing
chemical_list: D000199:Actins; D024061:Collagen Type III; D018840:HSP70 Heat-Shock Proteins; D018809:Proliferating Cell Nuclear Antigen