A 5 year old male child has multiple hyperprigmented macules over the trunk. On rubbing the lesion with the rounded end of a pen, he developed uicarial wheal, confined to the border of the lesion. The most likely diagnosis is

Darriers sign : uicarial wheal produced in a lesion after it is firmly rubbed with a finger or rounded end of a pen, the wheal is strictly confined to the borders of the lesion. Seen in uicarial pigmentosa, and rarely with cutaneous lymphoma or histiocytosiS FITZPATRICK TEXTBOOK OF DERMATOLOGY , PAGE 12.