Potential to improve analysis of the mechanisms of postinflammatory hyperpigmentation (PIH) and postinflammatory erythema (PIE) has been identified, according to commentary published in the British Journal of Dermatology.

In this study, 29 patients with skin phototypes II–VI and clinically confirmed truncal acne pustules were divided by propensity to develop pigmentation (PIH group, n=20) and those who were more prone to develop erythema (PIE group, n=9).

The investigators selected areas on the patients’ buttocks to receive trichloroacetic acid (TCA) concentrations of 20%, 25%, 30%, or 35%. Application of TCA was continued serially until the TCA 35% site frosted. The exact number of passes resulting in frosting at TCA 35% was used for the remaining concentrations at those sites to induce PIH/PIE without causing necrosis. The in vitro TCA-induced PIH model with acne-induced PIH/PIE was compared using the 6-point Investigator’s Global Assessment (IGA) of pigmentation and erythema in photographs processed with clinical polarized photography (CPP) and colorimetry.


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Concentration-dependent increases in IGA and CPP for pigmentation and erythema were achieved with controlled application of 20% to 30% TCA at all time points during the study. Investigators proposed that TCA 30% would be the optimum concentration to quantify the pigmentary response. With TCA 35%, both pigmentation and erythema scores were lower, but necrosis was already present at this concentration.

The main limitation of this study was the small sample size. “Future studies should include a broader range of skin phototypes, to explore other inciting factors of pigmentation and erythema such as ultraviolet radiation or visible light, to utilize a similar technique in other dermatological diseases with prominent pigmentary changes,” the study authors remarked.

The study is “a huge step forward in analyzing the mechanisms of PIH and PIE with a more controlled validation of the inciting agent and molecular characterization of the skin samples,” the study authors concluded. They suggest that research is needed to “confirm the therapeutic role of targeting miRNA-31 and miRNA-23 in the pigmentary process (eg, coincubation of melanocytes with a selective inhibitor of miRNA-31).”

Reference

Concha J, Afarideh M, Werth V. Postinflammatory hyperpigmentation and erythema: new insights into the pathogenesis Published online Dec 27, 2021. Br J Dermatol. doi.org/10.1111/bjd.20938