title: The prevalence and risk factors of post-inflammatory hyperpigmentation after fractional resurfacing in Asians.
abstract: BACKGROUND
  Ablative laser resurfacing is considered to be the main therapeutic option for the treatment of wrinkles and acne scarring. However, in Asians, post-inflammatory hyperpigmentation (PIH) is a common adverse effect of laser resurfacing. Fractional resurfacing is a new concept of skin rejuvenation whereby zones of micro thermal injury are generated in the skin with the use of a 1,540-nm laser. The risk and prevalence of hyperpigmentation in dark-skinned patients using this approach have not been studied.
  
  
  OBJECTIVE
  To assess the prevalence and risk factors of PIH that is associated with the use of fractional resurfacing in Asians.
  
  
  METHODS
  A retrospective study of 37 Chinese patients who were treated with fractional resurfacing for acne scarring, skin rejuvenation, and pigmentation was carried out. In all of the cases, pre- and post-treatment clinical photographs (from standardized and cross-polarized views) were taken using the Canfield CR system. Two independent observers assessed the photographs. A prospective study of treatments of nine different density and energy levels that were applied to the forearms of 18 volunteers was also performed. Clinical photographs were assessed pre- and post-treatment for evidence of PIH.
  
  
  RESULTS
  In the retrospective study, 119 treatment sessions were performed. Sixty-eight treatment sessions were high energy, low density; 51 sessions were low energy, high density. Patients who underwent a high energy but low-density treatment (range of energy 7-20 mJ; average energy 16.3 mJ, 1,000 MTZ) were associated with a lower prevalence of generalized PIH (7.1% vs. 12.4%) than those who underwent a low energy but high-density (range of energy 6-12 mJ; average energy 8.2 mJ, 2,000 MTZ) treatment. However, the difference was not statistically significant. Localized PIH occurred in the peri-oral area among patients who did not receive air cooling as an adjunctive therapy.
  
  
  CONCLUSIONS
  Both the density and energy of the treatment determines the risk of PIH in dark-skinned patients. Density may be of more important but further studies are necessary to determine this. Cooling to prevent bulk tissue heating is also important, especially in small anatomical areas. By using adequate parameters, the risk of PIH in dark-skinned patients can be significantly reduced.
authors.affiliation: Division of Dermatology, Department of Medicine, University of Hong Kong, Hong Kong SAR, China. hhlchan@hku.hk
authors.forename: Henry H L
authors.initials: HH
authors.lastname: Chan
authors.forename: D
authors.initials: D
authors.lastname: Manstein
authors.forename: C S
authors.initials: CS
authors.lastname: Yu
authors.forename: S
authors.initials: S
authors.lastname: Shek
authors.forename: T
authors.initials: T
authors.lastname: Kono
authors.forename: W I
authors.initials: WI
authors.lastname: Wei
mesh_terms: D000152:Acne Vulgaris / Q000150:complications; D044466:Asian People; D002921:Cicatrix / Q000209:etiology / Q000628:therapy; D017679:Cryotherapy; D003872:Dermatitis / Q000209:etiology* / Q000517:prevention & control; D005542:Forearm; D006801:Humans; D017495:Hyperpigmentation / Q000209:etiology* / Q000517:prevention & control; D010789:Phototherapy / Q000009:adverse effects* / Q000379:methods; D011446:Prospective Studies; D012189:Retrospective Studies; D012307:Risk Factors; D012720:Severity of Illness Index; D012867:Skin / Q000528:radiation effects; D015595:Skin Aging / Q000528:radiation effects