Extra-facial melasma: clinical, histopathological, and immunohistochemical case-control study

Extra-facial melasma is a prevalent dermatosis in some populations with special characteristics in relation to its clinical aspects and probable etiopathogenic factors. Few studies have attempted to address this alteration of pigmentation, which has become a challenge in clinical Dermatology.

To assess the clinical histopathological and immunohistochemical characteristics of extra-facial melasma, comparing affected, and unaffected sites.

Case-control study with 45 patients in each group (melasma and disease-free volunteers), assessing their clinical characteristics. In 36 patients, biopsies were performed on the lesion and the normal perilesional skin. Specimens were stained with HE and Fontana-Masson, and melanocytes analysed by immunohistochemistry. Objective measurements were accomplished by a specifically designed image analysis software.

The melasma group had a mean age ± SD of 56.67 ± 8 years, the majority of them were women (86.7%) and 82.1% of the female cases had reached menopause. There were no significant differences between groups in terms of presence of comorbidities, use of medications or hormone therapies. For extra-facial melasma patients, family history of this dermatose and of previous facial melasma was significantly higher than in the control group (P < 0.05). The HE staining showed increased rectification and basal hyperpigmentation, solar elastosis, and collagen degeneration in the pigmented area (P < 0.05). There was a significant increase in melanin density in melasma biopsies, but the immunohistochemical tests did not detect a difference between the groups in terms of number of melanocytes.

Extra-facial melasma appears to be related to menopause, family history, and personal history of facial melasma, in the studied population. Histopathology revealed a pattern similar to what has been described for facial melasma, with signs of solar degeneration, and a similar number of melanocytes, when comparing patients, and controls, suggesting that the hyperpigmentation is most likely the result of abnormal melanin production or distribution.