Application of a pigment measuring device--Mexameter--for the differential diagnosis of vitiligo and nevus depigmentosus.

BACKGROUND/PURPOSE Vitiligo and nevus depigmentosus (ND) present similar hypopigmented macules with significantly different prognoses. Although the distinction between the two diseases is important, differential diagnosis relies on medical history and physical examination, which is far from decisive in some cases. The Mexameter is an objective skin color-measuring device, and has been reported to provide a reproducible and sensitive means of quantifying small skin color differences. In this study, we investigated the usefulness of a Mexameter for discriminating these diseases. METHODS A selection of 202 hypopigmented skin lesions (182 from vitiligo and 20 from ND) were the objects of this study. Using a Mexameter, MIs were obtained from lesions and symmetrically located control skin. RMIs, ratios of the MIs of lesional skins to control skins, were calculated. RESULTS The mean MIs and RMIs were significantly different for vitiligo and ND. The mean RMI of ND lesions was 74+/-13, which was significantly higher than that of vitiligo lesions (50+/-24). No ND lesion had an RMI of <50%. CONCLUSION This study shows that the Mexameter, an objective pigment-measuring device, can be used to achieve a more accurate diagnosis of hypopigmentary disorders, and that the relative melanin index (RMI), which represents the relative pigment levels, might be a more effective parameter than the melanin index (MI) itself for comparing pigmentation differences.