What could be the cause of a small clear single lesion on the labia and painful intercourse?

Small Clear Single Lesion on Labia with Painful Intercourse

The most likely diagnosis is lichen sclerosus, which characteristically presents as porcelain-white papules or plaques on the labia minora and interlabial sulci, causing dyspareunia when erosions or fissures develop. 1

Primary Differential Diagnosis

Lichen Sclerosus (Most Likely)

• Presents as porcelain-white papules and plaques with areas of ecchymosis affecting the interlabial sulci, labia minora, clitoral hood, and perineal body 1, 2
• The main symptom is itch (worse at night), but pain and dyspareunia occur specifically when erosions or fissures are present 1
• Has a bimodal age distribution with peaks in prepubertal girls and postmenopausal women 1, 2, 3
• May have an autoimmune etiology with associations to other autoimmune diseases 2, 3
• Carries a 3.5-5% risk of malignant transformation to squamous cell carcinoma, requiring long-term surveillance 3

Infectious Causes to Exclude

• Herpes simplex virus causes painful ulcerations (not typically described as "clear lesions") with accompanying vulvar swelling 1, 2
• Bartholin gland infections present with swelling, erythema, and tenderness extending into the labia minora, commonly caused by gonorrhea and chlamydia 1, 2
• Syphilis manifests as flesh-colored papules (condylomata lata) that may be confused with warts 1

Traumatic Causes

• Vulvar hematomas from vigorous intercourse present with acute swelling and pain, typically involving the labia majora more than minora 4
• These are hemorrhagic fluid collections, not clear lesions 4

Diagnostic Approach

Mandatory Initial Steps

• Biopsy of the affected area is the first-line diagnostic test to confirm lichen sclerosus and rule out squamous cell carcinoma 3
• Document duration, pattern of symptoms, and any periods of remission 3
• Distinguish between pruritus versus pain with erosions/fissures 3

Physical Examination Findings

• Perform sequential pressure testing with a cotton swab to assess for focal erythema or pain (vulvodynia pattern) 5, 6
• Single-digit vaginal examination identifies tender pelvic floor muscles 5
• Bimanual examination assesses for uterine retroversion and pelvic masses 5
• In lichen sclerosus, look specifically for follicular delling, hyperkeratosis, and ecchymosis as signs of active disease 1

Required Laboratory Testing

• STI testing including gonorrhea and chlamydia nucleic acid amplification tests, particularly if gland involvement is suspected 3
• Viral culture for HSV when ulcerations are present, and serologic testing for syphilis if papules are present 3
• Baseline CBC and metabolic panel to assess for potential complications 3

Treatment Algorithm

For Confirmed Lichen Sclerosus

The accepted first-line treatment is ultrapotent topical corticosteroid clobetasol propionate ointment 1

Specific Regimen

• Apply clobetasol propionate once nightly for 4 weeks 1
• Then alternate nights for 4 weeks 1
• Then twice weekly for the final month 1
• The rationale for once-daily application is based on pharmacodynamic studies showing ultrapotent corticosteroids require only once-daily dosing 1

Management of Complications

If Introital Narrowing Causes Dyspareunia

• Surgery may be needed using part of the posterior vaginal wall in reconstruction to prevent further adhesions 1
• Topical steroids with vaginal dilators must be used postoperatively to prevent readhesion 1
• Start topical steroid 48 hours postoperatively once daily until fully epithelialized 1

If Neuropathic Pain Persists (Vulvodynia)

• This represents neuropathic pain that does not respond to topical corticosteroids 1
• Try xylocaine 5% ointment first 1
• Progress to amitriptyline in unresponsive cases 1

Critical Pitfalls to Avoid

• Do not dismiss ecchymosis in prepubertal girls as definitively indicating sexual abuse without considering lichen sclerosus, though lichen sclerosus can coexist with abuse due to Koebner phenomenon 1, 2
• Always assess for STI pathogens when Bartholin or Skene gland infections are present 1, 2
• If treatment appears to fail, consider: noncompliance (patients may be alarmed by package warnings against anogenital corticosteroid use), incorrect diagnosis requiring biopsy, or superimposed contact allergy requiring patch testing 1
• Pregnancy improves symptoms and signs, and normal vaginal delivery is usually possible 1
• Long-term surveillance is mandatory due to malignancy risk 3