A 52-year-old woman presents with painful erosions on the buccal mucosa and a reticular pattern of lesions on her wrists and forearms. Clinical examination reveals violaceous, flat-topped papules with Wickham's striae. Which investigation is most appropriate to confirm the diagnosis of lichen planus?

Explanation

## Diagnosis of Lichen Planus: Role of Skin Biopsy **Key Point:** Skin biopsy with histopathological examination is the gold standard and investigation of choice for confirming lichen planus, particularly when clinical diagnosis is uncertain or atypical variants are suspected. ### Histopathological Features of Lichen Planus The classic microscopic findings include: 1. **Hyperkeratosis** — thickened stratum corneum 2. **Hypergranulosis** — prominent granular layer 3. **Acanthosis** — irregular acanthosis with sawtooth pattern of rete ridges 4. **Lichenoid infiltrate** — dense band-like lymphocytic infiltration in the superficial dermis 5. **Basal cell degeneration** — liquefactive degeneration (apoptosis) of basal keratinocytes 6. **Absence of spongiosis** — distinguishes it from other inflammatory dermatoses **High-Yield:** The **sawtooth appearance of rete ridges** and **band-like lymphocytic infiltrate** are pathognomonic for lichen planus and confirm the diagnosis definitively. ### Why Biopsy is Superior in This Case Although the clinical presentation (violaceous papules, Wickham's striae, oral erosions) is highly suggestive, biopsy is essential to: - Rule out lichenoid drug reactions (morphologically identical) - Exclude lichen planus pemphigoides (requires DIF for confirmation) - Assess for malignant transformation in oral lichen planus - Confirm diagnosis in erosive or atypical variants **Clinical Pearl:** Wickham's striae (white reticular pattern visible on the surface) are a clinical hallmark but not pathognomonic; histology is required for definitive diagnosis. ### Biopsy Technique - **Site selection:** Sample from an active lesion (not old or resolving) - **Specimen:** Full-thickness skin including dermis - **Staining:** Routine H&E (hematoxylin & eosin) is sufficient for diagnosis - **Additional stains:** PAS may highlight the basement membrane zone; immunohistochemistry rarely needed **Mnemonic:** **SLAB** — **S**awtooth rete, **L**ichenoid infiltrate, **A**canthosis, **B**asal degeneration = Lichen planus histology