What is the cause of vitiligo involving the vulva in a 20-year-old patient?

Vitiligo is Caused by Autoimmune Lymphocytic Attack Against Melanocytes

The cause of vitiligo affecting the vulva in a 20-year-old patient is an autoimmune lymphocytic attack against melanocytes. 1

Pathophysiology of Vitiligo

Vitiligo is an acquired chronic depigmentation disorder characterized by white patches that result from the destruction of melanocytes. The evidence strongly supports an autoimmune etiology:

• The British Journal of Dermatology guideline clearly identifies that vitiligo is an autoimmune disease where melanocytes are destroyed by a specific immune response 1
• Patients with vitiligo often develop other autoimmune diseases, with approximately 32% having a family history of autoimmune disease 1
• In one study of 41 adults with vitiligo, 34% had autoimmune thyroid disease, suggesting a strong autoimmune association 1

Key Immunological Mechanisms

The autoimmune process in vitiligo involves:

• CD8+ T cell-driven immune response specifically targeting melanocytes 2
• A γ-interferon signature that contributes to melanocyte destruction 2
• Presence of circulating antibodies and T lymphocytes that react against melanocyte antigens 3

Distinguishing from Other Potential Causes

The other suggested causes in the question can be ruled out:

1. Malignant changes of keratocytes - This is not associated with vitiligo. Vitiligo involves the destruction of melanocytes, not malignant transformation of keratocytes 1

2. Allergic reaction from ingested drugs - While certain medications can cause hypopigmentation, true vitiligo is not caused by drug allergies. The British guideline does not list drug reactions as a primary cause of vitiligo 1

3. Result from overuse of irritants locally - Local irritants may trigger vitiligo in predisposed individuals (Koebner phenomenon), but they are not the primary cause. The guideline notes that vitiligo can Koebnerize but this is a triggering factor, not the underlying cause 1

Clinical Presentation in Genital Vitiligo

When vitiligo affects the vulva, it presents with:

• Well-defined white patches without surface changes or redness 1
• The genital region is one of the common sites for vitiligo, along with fingers, wrists, axillae, and other body orifices 1
• No mucosal involvement (vagina and cervix are spared) 1

Differential Diagnosis for Genital Vitiligo

When evaluating white patches on the vulva, important differentials include:

• Lichen sclerosus - This is an important differential diagnosis for genital vitiligo 1
• Postinflammatory depigmentation
• Pityriasis versicolor - This can be distinguished by KOH preparation showing "spaghetti and meatballs" appearance 4

Diagnostic Approach

Wood's light examination is helpful in diagnosing vitiligo, particularly in patients with lighter skin types:

• It delineates areas of pigment loss that may not be visible to the naked eye 1
• It can help demonstrate the extent and activity of the disease 1

Associated Conditions

The autoimmune nature of vitiligo is further supported by its association with other autoimmune conditions:

• Autoimmune thyroid disease is particularly common 1
• Other autoimmune diseases like insulin-dependent diabetes mellitus may coexist 3

In conclusion, the evidence clearly supports that vitiligo affecting the vulva in a 20-year-old patient is caused by an autoimmune lymphocytic attack against melanocytes, which is the fundamental pathological process in this condition.