Blue Nevus Hidden within the Nevus of Ota.

A 3-year-old boy presented with bluish patch and scattered blue spots on the left side of his face. After several sessions of laser treatment, the azury patch in the periorbital area became even darker. Histopathology showed many bipolar, pigment-laden dendritic cells scattered in the papillary and upper reticular dermis. Immunohistochemically, these cells were positive for S100, SOX-10, melan-A, P16, and HMB-45. The positive rate of Ki-67 was less than 5%. Finally, the lesion was diagnosed with nevus of Ota concurrent with common blue nevus. Therefore, for cases of the nevus of Ota with poor response to laser treatment, the possible coexisting diseases should be suspected.