A 5 yr. old male child has multiple hyperpigmented macules over the trunk. On rubbing the lesion with rounded end of pen, he developed urticarial wheal, confined to border of lesion, most likely diagnosis is:
**Core Concept**
The question is testing the student's ability to recognize a dermatological condition characterized by hyperpigmented macules that exhibit a positive Darier's sign, a clinical feature where the lesion becomes urticarial upon rubbing.
**Why the Correct Answer is Right**
The Darier's sign is a characteristic feature of mastocytosis, a condition where there is an accumulation of mast cells in the skin. When the skin lesion is rubbed with the rounded end of a pen, the mast cells in the lesion release histamine, leading to the development of urticarial wheal. This reaction is confined to the border of the lesion due to the distribution of mast cells.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely a distractor representing a different condition, such as erythema multiforme, which does not typically exhibit a positive Darier's sign.
**Option B:** This option might represent a condition like pityriasis versicolor, which does not characteristically have a positive Darier's sign.
**Option C:** This option could represent a condition like lichen planus, which does not typically exhibit a positive Darier's sign.
**Clinical Pearl / High-Yield Fact**
Mastocytosis is a condition where the accumulation of mast cells in the skin can lead to a variety of symptoms, including urticaria, pruritus, and flushing. The Darier's sign is a specific clinical feature that can help diagnose this condition.
**Correct Answer:** D. Mastocytosis.