This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Naevi and vessel related disorders, Subject name: Dental
A 5 yr old male child has multiple hyperpigmented 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. Most likely diagnosis: 
Select and explain. 
A. FDE, B. LP, C. Uicaria pigmentosa, D. Uicarial vsaculitis
C: Uicaria pigmentosa
Answer: C: Uicaria pigmentosa 
Explanation: Gentle rubbing of a lesion causes local itching, erythema, and wheal formation after 2-5 minutes which may be present for 30 min or few hrs. This is the Darier's sign and is seen in uicaria pigmentosa.