Okay, let's tackle this question. The patient is a 5-year-old with multiple hyperpigmented macules on the trunk. When they rub the lesion with a pen, there's a urticarial wheal at the border. Hmm.

First, I need to think about skin conditions in children that present with hyperpigmented macules. The key here is the response to rubbing. The urticarial wheal suggests some kind of allergic or inflammatory reaction.

Lichen planus is a possibility, but usually affects adults more. Then there's lichenoid eruptions, but maybe that's not it. Oh wait, there's a condition called Lichen Striatus. It's a self-limiting skin condition that occurs in children, often with linear hyperpigmented lesions. Rubbing might cause a Darier's sign, where there's a wheal at the border. That rings a bell. Darier's sign is associated with Lichen Striatus.

Let me check other options. Maybe Tuberous Sclerosis? They have hypopigmented patches, not hyperpigmented. Or maybe something like Neurofibromatosis? They have café-au-lait spots, but again, not hyperpigmented macules with this reaction.

Another thought: Lichen Planus can have a Darier's sign too, but it's more common in adults. Lichen Striatus is a variant that's linear and occurs in children. The urticarial wheal when rubbed is a key feature. So the correct answer should be Lichen Striatus.

The other options like Lichen Planus or others don't fit the age and the specific reaction. So the diagnosis is Lichen Striatus. The clinical pearl here is remembering that Darier's sign is a key diagnostic feature of Lichen Striatus in children.

**Core Concept**
This question tests recognition of **lichen striatus**, a self-limiting lichenoid eruption in children. The **Darier's sign** (urticarial wheal at the border of a lesion after friction) is a hallmark of lichenoid eruptions, including lichen striatus and lichen planus.

**Why the Correct Answer is Right**
Lichen striatus presents as **linear hyperpigmented macules** along Blaschko’s lines, commonly in children. Rubbing the lesion causes **Darier’s sign**, where histamine release from mast cells triggers a **urticarial wheal** at the lesion’s periphery. This reaction is due to **basophil degranulation** or **mast cell activation** in the dermis, not true urticaria. The linear arrangement and age of the patient further support this diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** *Lichen planus* typically affects adults and presents with **pruritic, violaceous papules**, not hyperpigmented macules.
**Option B:** *Tuberous sclerosis* features **hypopigmented ash-leaf spots** and **adenoma sebaceum**, not hyperpigmented lesions with Darier’s sign.
**Option C:** *Neurofibromatosis* includes **café-au-lait macules** and **neurofibromas**, which lack Darier’s sign and urticarial response.

**Clinical Pearl / High-Yield Fact

✓ Correct Answer: C. Uicaria pigmentosa