Studying Postinflammatory Hyperpigmentation (PIH) on human skin (For Professionals)

• Postinflammatory hyperpigmentation (PIH) is a common problem in darker skin types and happens after injury or inflammatory dermatoses such as acne vulgaris.

• The authors sought to create a reproductible model in humans after inducing PIH on the trunk with trichloracetic acid 35% (TCA 35%) and comparing it with PIH induced by truncal acne.
  • 4 patients were treated with TCA 35% and followed for 8 weeks.
  • 4 patients with inflammatory acne vulgaris (pustules) were followed for 8 weeks
• Subjects were evaluated clinically with:
  • photography, diffuse reflectance spectroscopy (DRS), colorimetry
  • Investigator’s Global Assessment (IGA) scale (0: absence; 5: the most severe):
    • for pigmentation: no differences were observed between the 2 groups and the maximum PIH was reached at 4 weeks.
    • for erythema: Scores were similar between the 2 groups on D7, D14, D42 and D56
  • Punch biopsies of 4mm punch were done:
    • one from representative acne pustule and one from TCA treated site at the first visit (D1) as well as after 4 weeks (D28).
    • On D1:
      • acne pustules were characterized by perifollicular neutrophilic inflammation (acute inflammation)
      • TCA lesions had full thickness epidermal necrosis with perivascular and/or perifollicular lymphocytic inflammation.
    • On D28
      • both acne and TCA-induced PIH showed perifollicular/perivascular lymphocytic inflammation (chronic inflammation) and dermal fibrosis.

• Authors conclude that:
  • the similarity of IGA scores, together with the observation that chronic inflammation along with fibrosis was found in both acne and TCA-induced PIH suggests that TCA-induced PIH is reproducible model with which to study risk factors and to compare other treatment modalities for PIH.
  • Differences in cellular infiltrate did not seem to distinguish TCA from inflammatory-induced PIH outcome in predisposed individuals. Dermal melanophages may be an important component of PIH under both experimental conditions.

Contributors:

Dr Christophe HSU – dermatologist. Geneva, Switzerland

Source of Information: P Isedeh,1 ON Agbai,2 HW Lim,1 I Hamzavi1 and MS Matsui3 1Multicultural Dermatology Center, Henry Ford Hospital, Detroit, MI, 2Department of Dermatology, University of California-Davis, Sacramento, CA and 3Estee Lauder Co’s, Melville, NY. An in vivo model of postinflammatory hyperpigmentation. International Investigative Dermatology (IID) 2013 – Edinburgh, United Kingdom (UK).