It has been proposed that melasma is a photoageing skin disorder. The photoaged fibroblasts have been suggested as an important source of melanogenic factors which are involved in the regulation of pigmentation. To investigate whether melasma includes senescent cells, lesional and perilesional normal skin from 38 melasma patients was assessed using a cell senescence marker, p16INK4A. The results showed that lesional dermal skin had more p16INK4A‐positive senescent cells than perilesional skin. The impact of senescent fibroblasts was further investigated in a pilot study using radiofrequency (RF) intervention for melasma. It showed that the RF therapy decreased the number of senescent cells with increased expression of procollagen‐1, which were associated with reduced epidermal pigmentation. This leads us to the speculation that senescent fibroblasts may contribute to drive melasma and might be considered as a potential therapeutic target.

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Histological features of Riehl melanosis have rarely been compared between lesional and perilesional normal skin and have not been precisely described using quantitative or immunohistochemical analysis or electron microscopic findings. To investigate the histopathological and immunohistochemical features of lesional and perilesional normal skin of patients with Riehl melanosis, we retrospectively evaluated the electronic medical records and skin biopsy specimens of 48 patients with Riehl melanosis. In addition, electron microscopy was performed on 1 case. Fontana–Masson staining for melanin and immunohistochemical staining for Melan-A, NKI/beteb, tyrosinase, and microphthalmia-associated transcription factor were performed. Although the difference was statistically insignificant, melanin pigment was increased in the epidermis of lesional skin compared with that of perilesional normal skin in patients. The number of melanocytes and their activity were significantly increased in lesional epidermal skin. Melanin pigment was also significantly increased in the lesional dermis. Pigmentary incontinence, basal cell liquefaction, dilated vessels, epidermal spongiosis, and colloid bodies were found in the lesional skin as well as in the perilesional normal skin to a lesser extent. Under electron microscopy of 1 randomly selected subject, many fibrocytes contained numerous melanosome particles in the cytoplasm of the lesional dermis. In perilesional normal skin, fibroblasts also contained melanosome particles; however, the number of melanosome-containing cells was less than that in lesional skin. Riehl melanosis is characterized by increased epidermal melanocytes and pigmentation, primarily involving the dermis, with histologically typical changes at the interface. Unlike that in other pigmentary diseases, most perilesional normal-appearing skin in Riehl melanosis also shows typical histopathological changes, although to a lesser extent.

Xanthomas present clinically as eruptive, tuberoeruptive, tuberous, tendinous, or planar forms. Among these, eruptive xanthoma (EX) is characterized by sudden development of multiple, red-to-yellow papules, each less than 5 mm in diameter, on the extensor surface of the extremities and the buttock area. EX is often associated with severe hypertriglyceridemia, underlying diabetes, obesity, or excessive alcohol intake. Histologically EX is characterized by foamy cells, which are lipid-laden macrophages surrounded by lymphoid cells, histiocytes, and neutrophils; however, mucin deposition is not a typical feature. Herein, we report a rare case of xanthoma with diffuse, abundant mucin deposition.

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