What is the likely diagnosis for a patient presenting with severe vulvar pruritus, thin skin, and purpura on the vulva?

Diagnosis: Lichen Sclerosus

The most likely diagnosis is lichen sclerosus (Option A), based on the classic triad of severe vulvar pruritus, thin/atrophic skin, and purpura on examination. 1

Clinical Presentation That Confirms This Diagnosis

The combination of fragile, thinned atrophic skin with purpura (ecchymosis) is pathognomonic for lichen sclerosus and distinguishes it from the other differential diagnoses. 1, 2

• Lichen sclerosus characteristically presents with intractable pruritus as the primary symptom in 85-98% of female patients affecting the anogenital area 1
• Physical examination reveals fragile, thinned, and atrophic skin with patches or plaques, often in a figure-eight pattern around the vulva and anus 1, 2
• Purpura and ecchymosis develop due to the extreme fragility of the affected skin, with fissures and tears occurring with minimal trauma 1
• The skin takes on a porcelain-white appearance with time, though early disease may show only subtle discoloration 1, 2

Why the Other Options Are Incorrect

Allergic reaction (Option B) would present with acute onset erythema, edema, and vesiculation rather than chronic thin atrophic skin with purpura 2

Lichen simplex chronicus (Option C) presents with lichenified (thickened), not thinned skin, resulting from chronic scratching and rubbing 2

Vulvodynia (Option D) is a pain syndrome without visible skin changes—the presence of thin skin and purpura excludes this diagnosis 1, 2

Critical Next Steps

• Biopsy is mandatory if the diagnosis is uncertain, if there is suspicion of neoplastic change, or if the patient fails to respond to initial treatment 1, 2
• Histology will show hyperkeratosis with hyper granulosis, subepithelial stromal lichenoid inflammatory infiltrate, and homogenization of collagen in the upper dermis 1, 3
• Screen for associated autoimmune conditions, as 22% of patients with lichen sclerosus have concurrent autoimmune disease (thyroid disease, diabetes, vitiligo, alopecia) 1, 4

Treatment Priorities

Initiate ultrapotent topical corticosteroids (clobetasol propionate 0.05% ointment) immediately as first-line therapy, applied once daily for 3 months, then tapered to maintenance dosing 1, 2, 5

• Long-term maintenance therapy is required to prevent progression to scarring, architectural changes (labial fusion, buried clitoris, introital stenosis), and squamous cell carcinoma 1, 2, 5
• Untreated lichen sclerosus carries a 4-5% risk of progression to vulvar squamous cell carcinoma, making prompt diagnosis and treatment essential for mortality reduction 1
• Topical calcineurin inhibitors (tacrolimus 0.1%, pimecrolimus 1%) are second-line options for steroid-resistant disease 1, 5, 3

Common Pitfalls to Avoid

• Do not mistake signs of lichen sclerosus in prepubertal girls for sexual abuse—the purpura and fissuring can be confused, though trauma may trigger disease onset 1, 6
• Do not delay treatment waiting for biopsy results in classic presentations—begin ultrapotent topical corticosteroids immediately to prevent irreversible scarring 1, 2
• Ensure patients understand this is a chronic condition requiring lifelong monitoring, as symptoms may improve but the disease rarely resolves completely 1, 5
• Perform annual surveillance examinations even after symptom control, as malignant transformation can occur in asymptomatic patients 1, 5