At birth, this now 18-year-old man had what he was told was “only a birthmark.” In the years since, the lesion has darkened and become increasingly well-defined and raised. It is occasionally irritated.
His parents deny any history of seizures, skeletal problems, vision problems, or developmental disabilities in the patient or the family. All parties want the lesion removed.
A contiguous linear collection of brown-to-tan papules and nodules runs entirely across the left upper chest, ending on the left shoulder. It measures about 1 cm in width. On closer examination, many of the marks appear to be a mix of milia and comedones.
No similar lesions are seen elsewhere, and the patient’s type IV skin appears normal in all other respects.
What is the diagnosis?