A 13-week-old boy presents to the pediatric dermatology clinic for the evaluation of a dark lesion on his back, present since birth.
His mother states that the lesion covered most of his back since birth, and has continued to grow in size proportionally with the child.
On examination, there is a large brown-blue lesion covering much of the back, with areas of thickened papules and diffuse thin hairs throughout the lesion.
What is the diagnosis?
