Okay, let's tackle this question. The patient has a unilateral white skin lesion with leukotrichia. First, I need to recall what conditions present with white patches and hair changes. Leukotrichia refers to white hair, which can be a sign of depigmentation.

Unilateral lesions make me think of conditions that don't spread symmetrically. Vitiligo is a common depigmentation disorder, but it's usually bilateral. However, there are exceptions. Then there's pityriasis versicolor, which causes hypopigmented patches but typically on the trunk and doesn't involve hair. Tinea versicolor is another possibility, but again, the hair isn't affected.

Wait, leukotrichia is when the hair turns white. This is often seen in conditions where melanocytes are destroyed. Vitiligo definitely causes leukotrichia because the melanocytes are lost, leading to white skin and hair. Since vitiligo can be unilateral in some cases, that might fit here. Other conditions like lichen sclerosus or morphea might have similar features but usually don't involve the hair.

Another possibility is congenital conditions like piebaldism, but those are present from birth. The question mentions a person, so it's likely acquired. So the most probable diagnosis is vitiligo. The key points are the depigmentation and leukotrichia, which are classic in vitiligo. The other options like tinea versicolor don't have hair changes. So the answer should be vitiligo.

**Core Concept**
The question tests the diagnosis of acquired hypopigmentation disorders with associated hair changes. **Vitiligo** is characterized by depigmented skin patches and leukotrichia (white hair) due to autoimmune destruction of melanocytes. Unilateral distribution may occur but is less common than symmetrical involvement.

**Why the Correct Answer is Right**
Vitiligo results from T-cell-mediated destruction of melanocytes, leading to loss of melanin in skin and hair. Leukotrichia (white hair) is pathognomonic for vitiligo, distinguishing it from other hypopigmentation disorders. While most cases are bilateral, unilateral vitiligo (segmental type) exists, often following a dermatomal pattern.

**Why Each Wrong Option is Incorrect**
**Option A: Tinea versicolor** – Causes hypopigmented or hyperpigmented patches but spares hair; diagnosed by potassium hydroxide (KOH) prep showing hyphae.
**Option B: Pityriasis versicolor** – Same as tinea versicolor; no hair involvement.
**Option C: Morphea** – Presents with sclerotic plaques, not hypopigmentation or leukotrichia.
**Option D: Piebaldism** – Congenital condition with white forelock and patches, not acquired.

**Clinical Pearl / High-Yield Fact**
Vitiligo is the only hypopigmentation disorder associated with leukotrichia. Remember: **"White skin, white hair, autoimmune flair"** – vitiligo often coexists with thyroid disease or diabetes mellitus.

**Correct Answer: C. Vitiligo**

✓ Correct Answer: B. Piebaldism