Brown macules on a depigmented skin patch

A 4-year-old Hispanic male presents to the dermatology clinic. Although the patient presents for an unrelated dermatology complaint, on physical exam he is noted to have a white forelock, in addition to a depigmented patch with overlying brown macules on the midline abdomen.

The physical exam is negative for a broad nasal root or heterochromic irises. The patient is otherwise ...