(M2.DM.16.4694)
An 8-year old boy is brought to the pediatrician by his distraught mother who is concerned about "light spots" that first appeared 4 months ago and have been slowly expanding over different parts of his body. He is not bothered by these areas, and they do not itch, burn, or bleed. He has otherwise been well. There is no family history of this skin condition, though his mother has a history of hypothyroidism. His skin exam is notable for smooth, hypopigmented patches over his bilateral knuckles, knees, and inner thighs, as seen in Figure A. His exam is also notable for a tuft of leukotrichia over his occiput, as seen in Figure B. Which of the following will help to confirm the diagnosis?
QID:
107863