An in vivo model for post-inflammatory hyperpigmentation.
J Invest Dermatol
Background: Post-inflammatory hyperpigmentation (PIH) is an acquired hypermelanosis occurring after cutaneous inflammation. A validated, in vivo model of acne-induced PIH was previously established using 35% trichloracetic acid (TCA). We aim to determine the minimum TCA concentration that induces PIH that results in validated measurements that are most similar to acne-induced PIH. Methods: Thirty subjects (skin types I-VI) were enrolled; 20 had a history of PIH, and 10 had a history of post-inflammatory erythema with acne resolution. Study procedures have been completed by 25/30 subjects. At day 0, two acne papules were identified on the back and 35%, 30%, 25%, and 20% TCA was applied to the buttocks. At day 28, clinical photography, Investigator Global Assessment (IGA) of hyperpigmentation and erythema, and colorimetry were performed for all lesions and adjacent uninvolved sites.Results: For 25 subjects, IGA and colorimeter data for day 28 were analyzed with one way repeated measures ANOVA. There were no significant differences of IGA scores of hyperpigmentation between acne and 25% and 30% TCA-induced lesions. Colorimetry L* (lightness) found no significant difference between acne and 30% and 35% TCA-induced lesions. Colorimeter parameter a* (erythema) demonstrated similarities between acne and 35% TCA-induced lesions.Conclusion: Our results show that 25% TCA has the potential to induce PIH similar to acne without necrosis. A higher concentration TCA (35%) resulted in the erythema similar to acne. We suggest that TCA-induced changes could serve as a model for the study of PIH.