Background: The role of the senescent cells in pigmentary disorders such as melasma, senile lentigo, and vitiligo has been studied. However, the status of cellular senescence in idiopathic guttate hypomelanosis (IGH) in vivo has not been proved.
Objective: We investigated p16INK4a positivity in paired normal and lesional skin in the IGH and senile lentigo patients to evaluate cellular senescence.
Materials and methods: Fiftyeight patients with IGH and 5 patients with senile lentigo were enrolled. Immunohistochemical stain using p16INK4a and MART-1 was performed and the p16INK4a positive melanocytes and fibroblasts were counted. The IGH skins were classified by sun-exposed and unexposed skin; 44 were sun exposed skin such as face, neck, arm, and legs, and 14 were unexposed skin of trunk. Five patients with senile lentigo were biopsied in face.
Results: Expression of p16INK4a on melanocytes and fibroblasts showed age-dependent increase in both normal and lesion skins. There were significant increase in the number of p16INK4a positive melanocytes in the lesion compared to the normal skin (mean ± SD, 12.3±23.9 vs 3.4±6.6 per 100 melanocytes, p=0.005). Subgroup analysis of sun exposed group revealed that there were more p16INK4a positive melanocytes in lesion than the normal skin (15.3±26.4 vs 4.5±7.3 per 100 melanocytes, p=0.01). Whereas, there was no statistically significant difference p16INK4a melanocytes in unexposed skin.
Conclusion: p16INK4a positive melanocytes were observed in the sun-exposed skin by age dependent manner. The number of p16INK4a positive melanocytes was increased in the lesional skin of IGH, suggesting a role of senescent melanocytes in the development of IGH. Further study in the role of p16INK4a melanocytes on regulation of skin pigmentation would be necessary.
