Hair follicle nevus with hyperplasia of smooth and striated muscle.

We report a peculiar nevus which occurred on the left side of the chin of an 18-year-old male. It had been present for four years and had grown rapidly during the last year. Histologically, many hair follicles, smooth muscles, and striated muscles were found within the reticular dermis. The hair follicles were accompanied by mature sebaceous glands; numerous eccrine glands were seen in the middle and deep dermis. Immunohistochemical stain and phosphotungstic acid hematoxylin stain supported the fact that the muscles seen between the follicles were both smooth and striated. This nevus was considered to be a hair follicle nevus accompanied by hyperplasia of smooth muscles and striated muscles.