**Question:** A 13-year-old boy with patchy depigmented skin on the right flank and upper thigh in segmental distribution. The depigmentation started 1 year back but has been static for last 4 months. Mother reports use of topical steroids which was ineffective.

**Core Concept:** Segmental vitiligo is a type of depigmentation disorder that occurs in a segmental distribution pattern. It is characterized by patchy depigmentation that follows dermatomes and is often associated with a positive family history of vitiligo.

**Why the Correct Answer is Right:** The correct answer is **D** (Vitiligo) as it is a more accurate diagnosis compared to other options:

A: Vitiligo is ruled out as the depigmentation is not static, but rather progressive in most cases.
B: Vitiligo is ruled out as the skin lesions are static, suggesting no active disease progression.
C: Vitiligo is ruled out as the depigmentation is segmental, while lichen planus is a non-segmental disorder.

**Why Each Wrong Option is Incorrect:**

A. Lichen Planus (LP) - LP is a non-segmental dermatological disorder characterized by flat, violaceous papules on the palms, soles, and oral mucosa. LP is not static and usually presents with pruritus and a positive Koebner phenomenon.
B. Psoriasis - Psoriasis is not static and presents with well-defined, elevated, erythematous plaques with silvery scales. It is not segmental and is not associated with a positive family history.
C. Lichen Planus (LP) - As explained above, LP is a non-segmental disorder, not matching the segmental distribution of the case described.

**Clinical Pearls:**

1. Segmental vitiligo should be considered in cases of non-progressive, static depigmentation in a segmental distribution pattern, especially when associated with a positive family history of vitiligo.
2. A negative family history and progressive depigmentation typically point towards other causes like LP, psoriasis, or other autoimmune disorders.
3. A positive Koebner phenomenon is a strong clue for LP, while pruritus is a clue for psoriasis.
4. A segmental distribution with family history is important to consider segmental vitiligo in the differential diagnosis.

**Explanation of the Case:**

A 13-year-old boy presents with segmental depigmentation in the right flank and upper thigh. Given the patient's age, segmental vitiligo is considered first among differential diagnoses.

**Why Vitamin D Deficiency is not likely:**

Vitamin D deficiency is unlikely in this case as the segmental distribution and negative family history are against the typical presentation of Vitamin D deficiency-induced vitiligo. Vitamin D deficiency-induced vitiligo usually presents with symmetric and non-segmental distribution, with a positive family history.

**Case Discussion:**

A 13-year-old boy presents with depigmentation in the right