Okay, let's tackle this question. The patient is a 5-year-old boy with multiple hyperpigmented macules on the trunk. When rubbed with a pen's rounded end, he gets urticarial wheals confined to the lesion borders. The key here is the Darier's sign, which is a diagnostic clue for a specific condition.

First, I need to recall what conditions present with hyperpigmented macules and a positive Darier's sign. Darier's sign is when rubbing a lesion causes a wheal and flare reaction. This is characteristic of Darier disease, a genetic skin condition. But wait, Darier disease is usually present at birth or in early childhood, with greasy, warty papules, not macules. Hmm, maybe I'm mixing it up with something else.

Another possibility is Lichen planus. Lichen planus can have hyperpigmented lesions and Darier's sign. But Lichen planus typically has pruritic, violaceous papules, not macules. The age here is 5, which is possible, but the presentation is different.

Wait, there's also a condition called Lichen Striatus. It's a self-limiting skin eruption in children, often with linear hyperpigmented macules. But does it have Darier's sign? I'm not sure. Let me think again.

Oh! Another condition: Incontinentia Pigmenti. That's an X-linked dominant disorder with skin lesions progressing through different stages. But the Darier's sign isn't a feature there.

Wait, maybe this is related to a mast cell disorder. Urticaria pigmentosa, which is a form of cutaneous mastocytosis. The lesions are hyperpigmented macules or papules, and when rubbed, they show a Darier's sign due to mast cell degranulation releasing histamine. That makes sense. The urticarial wheal is due to histamine release from mast cells. In children, cutaneous mastocytosis is more common and often presents with these lesions. The Darier's sign is a hallmark here.

So the correct answer should be Urticaria Pigmentosa (Cutaneous Mastocytosis). Let me check the options. The options weren't provided, but based on the question, the answer is likely Urticaria Pigmentosa. The other options (like Lichen Planus or Darier's disease) don't fit the Darier's sign as a key feature. Darier's disease is a keratinization disorder with greasy papules, not macules. Lichen Planus has papules and Darier's sign isn't typical. So the correct diagnosis here is Urticaria Pigmentosa.

**Core Concept**
The question assesses recognition of **urticaria pigmentosa**, a form of cutaneous mastocytosis. The key diagnostic clue is **Darier's sign**, where rubbing a lesion induces a wheal due to mast cell degranulation and histamine release. This condition is most common in children and presents as hyperpigmented macules.

**Why the Correct Answer is Right**
Urticaria pigmentosa is characterized by **hyperpigmented macules** (brownish lesions) that develop a **urticarial wheal** (Darier’s sign) upon friction. This reaction occurs because mast cells in the lesions release **hist

✓ Correct Answer: C. Uicaria pigmentosa