Abstract
Melasma is a common acquired hypermelanosis that affects sun-exposed areas of the skin, especially the face. Its histologic manifestations are evident in the epidermis, extracellular matrix, and dermis. One of the hallmarks of melasma is an increase in the amount of epidermal melanin; however, whether melanocyte numbers increase or not is a topic of debate. Interestingly, basement membrane abnormalities also characterize melasma. Furthermore, solar elastosis is recognized as one of the dermal pathologic findings of melasma. These findings suggest that extracellular matrix abnormalities are consistently found in melasma. In the dermis, increased vascularity and increases in mast cell numbers are observed, indicating that dermal factors have important roles in the pathogenesis of melasma, despite melasma being characterized by epidermal hyperpigmentation. This review discusses these histologic characteristics of melasma, and it considers their implications for the pathogenesis of this skin condition.
Highlights
Melasma is an acquired hypermelanosis characterized by the development of symmetrical, irregular light-to-dark brown macules and patches on sun-exposed areas of the skin, especially on the skin of the face [1]
This review discusses five histologic characteristics of melasma, namely, epidermal hyperpigmentation, basement membrane disruption, solar elastosis, increased vascularization, and a high prevalence of mast cells, and it considers their implications for the pathogenesis of melasma
Their study involved the quantitative image analysis of 56 Fontana-Masson-stained sections. They showed that, compared with perilesional normal skin, the number of melanocytes per millimeter of epidermal length and the number of melanocytes per millimeter of rete ridge length increased by 24% and 27%, respectively, in melasma skin, while the pigmented area per millimeter of epidermal length and the pigmented area per millimeter of rete ridge length increased by 73% and 39%, respectively
Summary
Melasma is an acquired hypermelanosis characterized by the development of symmetrical, irregular light-to-dark brown macules and patches on sun-exposed areas of the skin, especially on the skin of the face [1]. It is common among Asian and Hispanic women who are in their third or fourth decades of life [2]. Three patterns of melasma are recognized clinically that are based on the distribution of the hyperpigmentation on the face, namely, the centrofacial, malar, and mandibular patterns. Melasma often presents as a mixture of these patterns. The pathogenesis of melasma has not yet been fully elucidated. This review discusses five histologic characteristics of melasma, namely, epidermal hyperpigmentation, basement membrane disruption, solar elastosis, increased vascularization, and a high prevalence of mast cells, and it considers their implications for the pathogenesis of melasma
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