## Histopathology of Lichen Planus **Key Point:** The hallmark histological triad of lichen planus consists of: 1. **Hyperkeratosis** (thickened stratum corneum) 2. **Saw-tooth pattern of acanthosis** (irregular, pointed rete ridges) 3. **Band-like (lichenoid) lymphocytic infiltrate** in the superficial dermis that obscures the dermoepidermal junction ### Additional Features - **Civatte bodies** (colloid bodies) — apoptotic keratinocytes in the basal layer - **Melanin incontinence** — pigment in dermal macrophages (explains post-inflammatory hyperpigmentation) - **Intact basement membrane** (unlike lupus erythematosus) ### Clinical Correlation - The saw-tooth pattern is pathognomonic and distinguishes LP from other papulosquamous disorders - Band-like infiltrate is dense and obscures the dermoepidermal interface **High-Yield:** The combination of hyperkeratosis + saw-tooth acanthosis + lichenoid infiltrate is diagnostic for lichen planus on histology. [cite:Robbins 10e Ch 25] 
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