A Case of Seborrheic Keratosis in an Adolescent: Quite Rare Disease in Japan.

A 19-year-old woman with three seborrheic keratosis on her right abdomen and five seborrheic keratosis on her both buttocks is presented. That developed at the age of five and two months prior to the visit. At our initial dermatological examination, we noticed three oval, well defined, brown tumors on her right abdomen, and several round, well defined, brown nodules on her both buttocks. Dermoscopy findings showed comedo-like openings, fissures, and ridges. Histopathological examination showed hyperkeratosis and pseudohorn cysts, and basaloid keratinocytes proliferation with no dysplastic cells. These findings were consistent with SK. She was treated by cryotherapy using a liquid nitrogen spray, and her tumors and nodules dropped off entirely. Juvenile-onset of seborrheic keratosis is quite rare in East Asian countries and needs to be differentiated from keratinocytic epidermal nevus.