A 52-year-old woman presents with a 3-month history of painful erosions on her buccal mucosa and gingiva. On examination, she has white reticular patches on the dorsal surface of the tongue and erosive lesions on the gums. She also reports pruritic purple papules on her flexural surfaces and inner wrists. Dermoscopy of the skin lesions shows Wickham's striae. She denies oral ulcers elsewhere and has no systemic symptoms. What is the most likely diagnosis?

Explanation

## Diagnosis: Oral Lichen Planus with Cutaneous Involvement ### Clinical Presentation This patient presents with the classic triad of lichen planus: 1. **Oral involvement**: White reticular (lacy) patches on buccal mucosa and tongue, with erosive lesions on gingiva 2. **Cutaneous involvement**: Purple papules on flexural surfaces (wrists, inner arms) 3. **Dermoscopic confirmation**: Wickham's striae (fine white lines on the surface of papules) ### Key Diagnostic Features **Key Point:** Lichen planus is an autoimmune T-cell mediated disorder affecting skin and mucous membranes. The oral form can occur with or without cutaneous manifestations. **High-Yield:** The pathognomonic finding is **Wickham's striae** — fine white lines visible on dermoscopy or under magnification, representing hyperkeratosis in the grooves of papules. ### Oral Lichen Planus Variants | Variant | Appearance | Symptoms | |---------|-----------|----------| | Reticular (most common) | Lacy white patches | Asymptomatic or mild | | Erosive | Painful erosions, ulcers | Severe pain, difficulty eating | | Atrophic | Thin, erythematous mucosa | Burning sensation | | Bullous | Fluid-filled blisters | Pain, rupture to erosions | **Clinical Pearl:** Erosive oral lichen planus is the most symptomatic form and carries a small risk (~1%) of malignant transformation to squamous cell carcinoma over 10+ years. ### Distinguishing Features from Differentials **Key Point:** The combination of Wickham's striae on dermoscopy, reticular white patches in the mouth, and purple papules on flexural surfaces is pathognomonic for lichen planus. **Mnemonic: "6 P's of Lichen Planus"** — Purple, Planar, Papules, Plaques, Polygonal, Pruritic (and Plaques on palms/soles, Papules on penis, Pain in oral form) ### Histopathology (if biopsy were done) Would show: - Saw-tooth pattern of hyperkeratosis - Dense band-like lymphocytic infiltrate in the dermis - Civatte bodies (colloid bodies) in the basal layer - Intact basement membrane (unlike pemphigus) ### Management Considerations - Topical corticosteroids (first-line for localized disease) - Intralesional corticosteroids for resistant lesions - Systemic corticosteroids or retinoids for severe erosive disease - Regular monitoring for malignant transformation in erosive oral lichen planus [cite:Robbins 10e Ch 25]