A 52-year-old woman presents with violaceous, polygonal papules on her wrists and lower legs with a lacy white pattern on the buccal mucosa. Which single feature best distinguishes lichen planus from lichen nitidus?

Explanation

## Lichen Planus vs Lichen Nitidus: Key Discriminator ### Clinical Presentation Comparison | Feature | Lichen Planus | Lichen Nitidus | |---------|---------------|----------------| | **Wickham's Striae** | Present (lacy white lines on mucosa and skin) | Absent | | **Lesion Size** | 1–10 mm (usually >1 mm) | <1 mm (pinpoint) | | **Mucosal Involvement** | Common (reticular, erosive) | Rare | | **Distribution** | Wrists, shins, genitalia | Generalized, dorsal hands | | **Color** | Violaceous, shiny | Flesh-colored, grayish | | **Pruritus** | Marked | Minimal | **Key Point:** The single best clinical discriminator is the **presence of Wickham's striae on mucosal surfaces**. Wickham's striae — the lacy, reticulate white lines seen on the buccal mucosa and skin surface of lichen planus lesions — are a pathognomonic feature of lichen planus and are **absent in lichen nitidus**. The stem itself describes the classic lacy white pattern on the buccal mucosa, directly pointing to this feature. ### Why Not the Other Options? - **Option A (Saw-tooth acanthosis):** This is a histological finding requiring biopsy. The question asks for a single distinguishing feature in a clinical context; histology is not a bedside discriminator. - **Option C (Lesion size >1 mm vs <1 mm):** While lesion size does differ between the two conditions, this is a quantitative and somewhat subjective clinical measure. More importantly, Wickham's striae are **pathognomonic** (specific) to lichen planus and are entirely absent in lichen nitidus, making them a more definitive single discriminator. - **Option B (Palms and soles):** Palmoplantar involvement can occur in both conditions and is not a reliable discriminator. ### Histopathology (High-Yield) - **Lichen planus**: Saw-tooth acanthosis, dense band-like lymphocytic infiltrate at the dermoepidermal junction, Civatte bodies, melanin incontinence - **Lichen nitidus**: Focal "ball-in-claw" lymphocytic infiltrate confined to 2–3 dermal papillae, minimal acanthosis **Clinical Pearl:** Wickham's striae result from focal hypergranulosis overlying the areas of lymphocytic infiltration. They are best seen on the buccal mucosa and can be accentuated by applying mineral oil to skin lesions. Their presence is considered pathognomonic for lichen planus (Andrews' Diseases of the Skin; Rook's Textbook of Dermatology). --- *Reference: Andrews' Diseases of the Skin, 13th ed.; Rook's Textbook of Dermatology, 9th ed.*