A 52-year-old woman presents with purple, polygonal papules on her wrists and shins with a lacy white pattern on the buccal mucosa. Histopathology shows a dense band-like lymphocytic infiltrate at the dermoepidermal junction with basal cell degeneration. All of the following are characteristic features of lichen planus EXCEPT:

Explanation

## Characteristic Features of Lichen Planus **Key Point:** Lichen planus is a T-cell mediated autoimmune disorder with distinctive clinical, histological, and immunofluorescence findings. The correct answer identifies what is NOT characteristic. ### Clinical Features - **Wickham's striae**: Fine white lacy lines visible on the surface of oral and cutaneous lesions — pathognomonic finding - **Koebner phenomenon**: Positive in ~25% of patients; new lesions appear at sites of trauma - **Distribution**: Flexural surfaces (wrists, forearms, shins, genitals), oral mucosa - **Morphology**: Purple, polygonal, pruritic papules; "6 P's" mnemonic (Purple, Polygonal, Papules, Plaques, Pruritus, Planar) ### Histopathology (Lichenoid Interface Dermatitis) 1. Dense band-like (lichenoid) lymphocytic infiltrate at dermoepidermal junction 2. Basal cell degeneration and apoptosis (colloid bodies) 3. **Saw-tooth** (acanthosis with pointed rete ridges) or **wedge-shaped** acanthosis 4. Hyperkeratosis and hypergranulosis 5. Absence of spongiosis (distinguishes from eczema) ### Immunofluorescence Findings | Feature | Finding | Significance | |---------|---------|---------------| | **Direct IF (DIF)** | Fibrinogen and fibrin at basement membrane zone (BMZ) | Characteristic; supports diagnosis | | **IgG/IgM deposition** | Usually absent or minimal at BMZ | NOT a typical finding | | **C3 deposition** | May be present but NOT granular at BMZ | Granular IgG/C3 is seen in bullous pemphigoid, not LP | **High-Yield:** Direct immunofluorescence in lichen planus shows **fibrinogen at the basement membrane zone**, NOT granular IgG and C3. Granular IgG and C3 deposition at the BMZ is characteristic of bullous pemphigoid and linear IgA disease, not lichen planus. ### Why This Matters - The question tests understanding of immunofluorescence patterns - Confusing LP's DIF pattern with bullous autoimmune disorders is a common trap - Fibrinogen deposition (not immunoglobulin) is the hallmark of LP on DIF **Clinical Pearl:** When you see "granular IgG/C3 at BMZ," think bullous pemphigoid or dermatitis herpetiformis — NOT lichen planus. [cite:Robbins 10e Ch 25]