A 42-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 oral mucosa with surrounding erythema and ulceration. She also complains of burning sensation while eating. On cutaneous examination, there are violaceous, flat-topped papules on her wrists and shins with a fine white network pattern. Her nails show longitudinal ridging and thinning. 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 affecting multiple sites: **Oral manifestations:** - White reticular (lacy) patches — pathognomonic Wickham's striae - Erosive/ulcerative form with mucosal erythema - Burning sensation and pain **Cutaneous manifestations:** - Violaceous (purple), flat-topped papules - Characteristic sites: flexural surfaces (wrists, shins) - Fine white network pattern on surface **Nail involvement:** - Longitudinal ridging and thinning - Indicates chronic, severe disease ### Key Diagnostic Features **High-Yield:** Lichen planus follows the **6 P's mnemonic:** - **P**urple - **P**apules - **P**lanar (flat-topped) - **P**olygonal - **P**laque - **P**ruritic (often, though this patient has pain) **Key Point:** Oral lichen planus is the most common site of involvement (60–70% of cases), and erosive oral disease indicates more severe systemic involvement. **Clinical Pearl:** The presence of Wickham's striae (white reticular pattern) on oral mucosa is virtually diagnostic of lichen planus and distinguishes it from other oral ulcerative conditions. ### Histopathology (if biopsy performed) - Saw-tooth pattern of hyperkeratosis - Dense lymphocytic infiltrate in a band-like distribution at the dermoepidermal junction - Civatte bodies (apoptotic keratinocytes) - Intact basement membrane (unlike pemphigus) ### Associated Conditions - Hepatitis C (especially in certain geographic regions) - Autoimmune thyroiditis - Systemic lupus erythematosus - Malignant potential: 0.5–5% risk of oral squamous cell carcinoma in erosive disease ### Management Approach 1. Topical corticosteroids (first-line for localized disease) 2. Systemic corticosteroids for extensive involvement 3. Retinoids or calcineurin inhibitors for resistant cases 4. Hepatitis C screening 5. Regular surveillance for malignant transformation in erosive oral disease