A 48-year-old man from Delhi presents with a 6-week history of painful erosions on his tongue and buccal mucosa. On examination, white reticular lines are visible on the oral mucosa, with areas of atrophy and erosion. He denies any skin lesions. A biopsy of the oral mucosa is performed. Histopathology shows a dense band-like lymphocytic infiltrate at the dermoepidermal junction with basal cell degeneration and Civatte bodies. What is the most likely diagnosis?

Explanation

## Diagnosis: Oral Lichen Planus (Erosive Variant) ### Clinical & Histopathologic Correlation This patient presents with **erosive oral lichen planus**, confirmed by: 1. **Clinical features** — reticular white lines with erosions on tongue and buccal mucosa 2. **Histopathology** — lichenoid interface dermatitis (hallmark finding) 3. **Absence of cutaneous lesions** — oral lichen planus can occur without skin involvement (oral-only form) ### Pathologic Hallmarks of Lichen Planus **Key Point:** The histologic triad of lichen planus is: 1. **Lichenoid interface dermatitis** — dense band-like lymphocytic infiltrate at the dermoepidermal junction 2. **Basal cell degeneration** — liquefactive necrosis of basal keratinocytes 3. **Civatte bodies** — apoptotic keratinocytes (eosinophilic, round bodies in the superficial dermis) **Mnemonic: LBC of LP Histology** — **L**ichenoid infiltrate, **B**asal cell degeneration, **C**ivatte bodies ### Oral Lichen Planus Variants | Variant | Appearance | Symptoms | Prognosis | | --- | --- | --- | --- | | Reticular | White lacy lines (Wickham's striae) | Asymptomatic or mild | Benign | | Atrophic | Erythematous, thin mucosa | Burning, pain | Moderate | | Erosive | Ulcerations with white borders | Severe pain, dysphagia | Higher malignant risk | | Bullous | Blisters on erythematous base | Painful erosions | Rare | ### Why Oral-Only Lichen Planus Occurs **Clinical Pearl:** Approximately 20–30% of lichen planus cases present with oral involvement alone, without cutaneous manifestations. This is thought to reflect local oral mucosal immunity and may be triggered by chronic irritation, contact allergens, or idiopathic autoimmunity. ### Pathophysiology ```mermaid flowchart TD A[T-cell mediated autoimmunity]:::outcome --> B[Activation of CD8+ T cells]:::action B --> C[Recognition of basal keratinocytes as antigen]:::action C --> D[Apoptosis of basal cells]:::action D --> E[Lichenoid infiltrate at DEJ]:::outcome E --> F{Severity?}:::decision F -->|Mild| G[Reticular/Atrophic form]:::outcome F -->|Severe| H[Erosive form with ulceration]:::outcome H --> I[Monitor for malignant transformation]:::urgent ``` ### Malignant Transformation Risk **High-Yield:** Erosive oral lichen planus carries a **0.5–5% risk of malignant transformation** to squamous cell carcinoma over 5–10 years. Risk factors include: - Erosive subtype (higher risk than reticular) - Chronic irritation - Smoking and alcohol use - Long disease duration **Warning:** Regular surveillance with clinical examination and biopsy of any suspicious areas is mandatory. ### Management of Erosive Oral LP 1. **Topical corticosteroids** — triamcinolone 0.1% paste or fluocinonide gel 2. **Antimicrobial rinses** — chlorhexidine to prevent secondary infection 3. **Systemic corticosteroids** — for severe, refractory cases 4. **Retinoids** — acitretin or isotretinoin for extensive disease 5. **Avoid irritants** — spicy foods, alcohol, smoking cessation