Nevus depigmentosus following the Blaschko lines with the robustly activated mTOR pathway

Nevus depigmentosus is defined as a congenital non-progressive hypopigmented macule.(1) We report a case of nevus depigmentosus following the Blaschko lines with robust activation of the mammalian target of rapamycin (mTOR) pathway. A 6-year-old Japanese boy was referred to us with asymptomatic hypopigmented linear lesions. The parents had noticed the lesions when the patient was 3 years old. The patient had no developmental delay or mental retardation. Physical examination revealed asymptomatic hypopigmented linear lesions along the lines of Blaschko on the right chest to the back and a linear lesion on the right arm (arrow) (Fig. 1a).