## Most Common Site of Cutaneous Lichen Planus **Key Point:** The flexural surfaces of the wrists, forearms, and lower legs are the most commonly affected sites in cutaneous lichen planus, accounting for >60% of cases. ### Distribution of Cutaneous Lichen Planus by Site | Site | Frequency | Clinical Features | Trauma Exposure | |------|-----------|-------------------|------------------| | **Flexural wrists & forearms** | >60% (Most common) | Violaceous papules, linear arrangement (Koebner phenomenon) | Moderate; friction from clothing | | Extensor elbows & knees | 30–40% | Papules, plaques; hyperkeratosis | High; frequent trauma | | Trunk and abdomen | 15–25% | Scattered papules; less symptomatic | Low; protected area | | Palms and soles | <5% | Hyperkeratotic papules; rare | Variable; thicker stratum corneum | **High-Yield:** Flexural surfaces (wrists, forearms, lower legs) are the **classic distribution** in cutaneous lichen planus. This predilection is due to: 1. **Koebner phenomenon:** Friction from clothing and minor trauma trigger lesion formation. 2. **Anatomical factors:** Thin epidermis on flexural surfaces facilitates immune cell infiltration. 3. **Moisture retention:** Flexural areas retain more moisture, promoting antigen presentation. ### Clinical Clues **Mnemonic:** **FWF** = **F**lexural **W**rists and **F**orearms — the most common site. **Clinical Pearl:** The **Wickham striae** (fine white lines visible on the surface of papules) are pathognomonic for lichen planus and are most easily appreciated on the buccal mucosa and flexural skin lesions. **Warning:** Do not confuse cutaneous lichen planus distribution with lichen nitidus (which favors dorsal hands and feet) or lichen sclerosus (which favors anogenital region). Each has a distinct predilection site.
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