O/E: 3.5 cm diameter hypopigmented macule with irregular border,
Diagnosis: This is probably a nevus depigmentosis. Nevus anemicus is less likely as is ash leaf macule of tuberous sclerosis. (I did not do dermoscopy of this lesion, but that would have been a good idea.
1. Oiso N, Kawada A. The diagnostic usefulness of dermoscopy for nevus depigmentosus. Eur J Dermatol. 2011 Jul-Aug;21(4):639-40. Free full text