Two patterns of solar lentigines: a histopathological analysis of 40 Japanese women

Solar lentigines are common acquired pigmented lesions on sun-exposed skin. Their histopathological features have been reported as large numbers of melanocytes at the base of clubbed and budding rete ridges. In this study, biopsies were taken from facial solar lentigines in 40 Japanese women, and the sections were stained using hematoxylin-eosin, Fontana-Masson, and immunostained for melanocytes and Langerhans cells in order to verify the histological patterns of Japanese patients. We characterized the histopathological features of solar lentigines on the face and identified two patterns: one pattern (20/40 cases) demonstrated a flattened epidermis with basal melanosis, and the other pattern (20/40 cases) showed epidermal hyperplasia with elongated rete ridges composed of deeply pigmented basaloid cells. We termed the former pattern the "flattened epidermis" group, and the latter the "budding" group, respectively. The flattened epidermis group showed a significantly thinner epidermis, more severe solar elastosis and fewer Langerhans cells in the epidermis as compared with the budding group. We concluded that more severely sun-damaged solar lentigines might show the changes observed in the flattened epidermis group. Langerhans cells in the epidermis of solar lentigines might play a role in the remission of postinflammatory pigmentation due to aesthetic treatment.