A 28-year-old woman presents with progressive loss of skin colour over her hands and face for the past 8 months. On examination, the lesions marked **A** in the diagram show sharply demarcated chalk-white depigmented patches with no scale or sensory loss. Wood's lamp examination reveals bright blue-white fluorescence. She reports a family history of thyroid disease. Which of the following autoimmune conditions is MOST commonly associated with this presentation and should be screened for first?

Question

Accepted Answer

D. Autoimmune thyroid disease (Hashimoto or Graves disease). ## Why Autoimmune thyroid disease is right

The sharply demarcated chalk-white depigmented patches marked **A** are pathognomonic for vitiligo, a chronic acquired autoimmune depigmenting disorder caused by selective CD8+ T-cell-mediated destruction of epidermal melanocytes. Autoimmune thyroid disease (Hashimoto thyroiditis and Graves disease) is the MOST COMMON autoimmune association with vitiligo, occurring in a significant proportion of vitiligo patients. Current guidelines recommend TSH and anti-TPO screening in all vitiligo patients. The patient's family history of thyroid disease further elevates this risk. Per Rook's Textbook of Dermatology, 10th ed, autoimmune thyroid disease is the most frequently encountered polyglandular autoimmune association in vitiligo.

## Why each distractor is wrong

- **Type 1 diabetes mellitus**: While associated with vitiligo as part of polyglandular autoimmune syndromes, it is less common than autoimmune thyroid disease and is not the first-line screening priority.
- **Addison disease**: This is a recognized but less frequent autoimmune association with vitiligo compared to thyroid disease; screening is not routine in all vitiligo patients.
- **Pernicious anaemia**: Although part of the autoimmune spectrum in vitiligo, it is significantly less common than thyroid disease and does not warrant first-line screening.

**High-Yield:** Screen ALL vitiligo patients with TSH and anti-TPO for autoimmune thyroid disease — the most common systemic autoimmune association.

[cite: Rook's Textbook of Dermatology, 10th ed; IADVL Textbook of Dermatology, 5th ed]

Answer

A. Type 1 diabetes mellitus

Answer

B. Addison disease

Answer

C. Pernicious anaemia

Explanation

Why Autoimmune thyroid disease is right

Why each distractor is wrong

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