Postinflammatory hyperpigmentation (PIH) commonly occurs, but the histopathological features are not well characterized.Methods
A total of 21 PIH patients' medical charts were reviewed. Punch biopsies from lesional and perilesional normal skin were performed. Sections were stained with hematoxylin-eosin, Fontana-Masson, NKI/beteb, microphthalmia-associated transcription factor (MITF), CD68, c-kit, factor XIIIa, MMP-2 and MMP-9.Results
Fontana-Masson-stained sections suggested two obvious PIH groups: epidermal (13 cases) and dermal (8 cases) pigmentation. The epidermal pigment group had increased epidermal basal pigmentation. The dermal pigment group had marked pigmentation within the upper dermis and decreased epidermal pigmentation. More intense perivascular lymphocytic infiltration was observed in the dermal pigment group. NKI/beteb levels were increased in lesional skin in both groups. The numbers of MITF+ melanocytes were not different between lesional and perilesional normal skin in either group. The expression of CD68 and c-kit was significantly higher in the dermis of lesional skin than in normal skin in the dermal pigment group. MMP-2 expression was upregulated in lesional skin in both groups.Conclusion
PIH patients can be classified into two histopathological groups: epidermal and dermal pigmentation. The dermal pigment group showed decreased levels of epidermal pigmentation. This study provides histopathological information that can improve the treatment of PIH.