A new morphometric technique for assessment of melanization in skin of guinea pigs

BACKGROUND: The degree of melanization is an important finding in many skin disorders. An objective measurement of melanin density is needed to achieve an accurate evaluation. OBJECTIVES: The present work aims at translating the subjective increase of melanin particles after narrow band ultraviolet-B (NB-UVB) irradiation into objective numerical values ready for statistical analysis. MATERIALS AND METHODS: This study had involved 18 guinea pigs that were exposed to biweekly sessions of NB-UVB radiation for 4 weeks to induce skin pigmentation. Two skin biopsies were obtained from each animal; the first before treatment and the second at the end of the study, using 5 mm punch and stained with hematoxylin and eosin and Masson-Fontana (MF) stains. Surface area of both the epidermis (ESA) and the melanin particles (MPSA) were measured in μm(2) using a software supplied with Olympus light microscope. The MPSA/ESA percentage was calculated for each biopsy. The results before and after NB-UVB exposure were compared and statistically analyzed. RESULTS: In the MF-stained sections, the mean ± SD of the MPSA/ESA percentage were 0.24 μm(2) ± 0.09 and 6.21 μm(2) ± 2.45 at the start of the study and at its end, respectively, with a highly significant difference (P < 0.001). CONCLUSION: This technique offers a new methodology for an accurate numerical evaluation of epidermal melanization.