Heterogeneous Pathology of Melasma and Its Clinical Implications

Abstract

Melasma is a commonly acquired hypermelanosis that affects sun-exposed areas of the skin, with frequent facial involvement. Its histologic manifestations are evident in the epidermis, extracellular matrix, and dermis. In addition to epidermal pigmentation, pathologic findings of melasma include extracellular matrix abnormality, especially solar elastosis. The disrupted basement membrane has been described in melasma with variable incidences. In the dermis, an increase in vascularity and an increase in the number of mast cells were observed, indicating that dermal factors have critical roles in the pathogenesis of melasma, despite the fact that melasma is characterized by epidermal hyperpigmentation. This review discusses such histologic characteristics of melasma, with consideration to their implications for melasma treatment.

Keywords: basement membrane; histopathology; mast cells; melasma; photoaging; vascularization.

Figure 1

The role of mast cells in melanogenesis and photoaging. UV= ultraviolet; MMPs = matrix metalloproteases; VEGF = vascular endothelial growth factor; FGF-2 = fibroblast growth factor-2; TGF-β = transforming growth factor-β; ECM = extracellular matrix; BM = basement membrane.

Figure 2

Histologic changes after eight weeks of treatment with tranexamic acid. (A,B) Fontana–Masson staining shows reduced epidermal pigmentation (×100); (C,D) Anti-CD31 staining shows reduced levels of vascularity (×100); and (E,F) Antitryptase staining shows reduced mast cell numbers (×100). Reproduced from [31].