Nevus achromicus and Nevus anemicus can be differentiated by:
Lesions in Nevus depigmentosus will not increase in size as the borders does not merge into surrounding skin on Diascopy. (Pressing with a glass slide)
Whereas borders get merged and there will be increase in size in Nevus anemicus, on Diascopy.
Hypopigmented lesions
Immunofluroscence
Diascopy
Huctchinson's sign