A 38-year-old man from rural Maharashtra presents with a 6-month history of itchy, flat-topped purple papules on his forearms, shins, and genitals. He also complains of white patches inside his mouth that are asymptomatic. On examination, the skin lesions are polygonal, violaceous, and arranged in a linear pattern over areas of trauma (Koebner phenomenon). Oral examination reveals a reticular pattern of white lines on the buccal mucosa. He denies any systemic symptoms or recent drug intake. What is the most appropriate next step in management?

Explanation

## Management of Lichen Planus: Diagnosis and Treatment Strategy ### Clinical Diagnosis This patient has **classic lichen planus** with: - **Cutaneous features**: Purple, polygonal, flat-topped papules with Koebner phenomenon - **Oral features**: Reticular white patches (Wickham's striae pattern) - **Distribution**: Typical sites (flexural surfaces, genitals, oral mucosa) **Key Point:** The diagnosis of lichen planus is primarily **clinical** based on morphology and distribution. Biopsy is confirmatory but not always necessary if the clinical picture is classic. ### Why Biopsy Is NOT the Best First Step While biopsy would confirm the diagnosis histologically (saw-tooth hyperkeratosis, band-like lymphocytic infiltrate, Civatte bodies), it is: - **Not necessary** when the clinical diagnosis is clear and unambiguous - **Invasive** and causes scarring (problematic in a patient with Koebner phenomenon) - **Not required** to initiate treatment **Warning:** In a patient with Koebner phenomenon, a biopsy may provoke new lesions at the biopsy site. ### Appropriate Management Strategy **High-Yield:** First-line treatment for localized lichen planus is **topical corticosteroids** (potent agents like clobetasol 0.05% cream for skin; triamcinolone 0.1% paste for oral lesions). #### Treatment Algorithm for Lichen Planus ```mermaid flowchart TD A[Lichen Planus Diagnosed]:::outcome --> B{Extent & Severity?}:::decision B -->|Localized, mild-moderate| C[Topical Corticosteroids]:::action B -->|Extensive or refractory| D[Intralesional Corticosteroids]:::action B -->|Severe, systemic involvement| E[Systemic Corticosteroids or Retinoids]:::action C --> F[Monitor for Response]:::action D --> F E --> F F --> G{Oral Involvement?}:::decision G -->|Yes| H[Topical steroid paste + Regular monitoring]:::action G -->|No| I[Routine follow-up]:::action H --> J[Screen for malignancy if erosive]:::urgent ``` ### Why the Correct Answer Is Best **Prescribe topical corticosteroids and monitor for oral malignancy** is the most appropriate next step because: 1. **Topical corticosteroids** are first-line for localized cutaneous and oral lichen planus - Potent topical steroids (clobetasol 0.05%) for skin lesions - Triamcinolone 0.1% paste or fluocinonide gel for oral lesions - Effective in 60–80% of patients 2. **Monitoring for oral malignancy** is essential because: - Erosive oral lichen planus carries a **0.5–1% risk** of malignant transformation to squamous cell carcinoma - This patient has oral involvement (reticular patches) - Long-term follow-up with clinical examination is mandatory - Biopsy of any suspicious lesions (erythema, ulceration, induration) should be performed **Clinical Pearl:** Erosive oral lichen planus has higher malignancy risk than reticular (non-erosive) form. This patient has reticular patches, but regular surveillance is still warranted. ### Why Systemic Corticosteroids Are NOT First-Line **Key Point:** Systemic corticosteroids are reserved for: - Extensive cutaneous involvement unresponsive to topical therapy - Severe erosive oral lichen planus - Generalized disease affecting quality of life For a patient with localized disease (forearms, shins, genitals, oral), topical therapy is preferred to minimize systemic side effects. ### Why Antimalarials Are NOT First-Line Antimalarials (hydroxychloroquine, chloroquine) are used for: - Lichen planus unresponsive to corticosteroids - Chronic, recurrent disease - As steroid-sparing agents They are **second-line**, not first-line therapy. ### Monitoring and Follow-Up | Aspect | Action | |--------|--------| | Cutaneous lesions | Assess response to topical steroids at 4–6 weeks | | Oral lesions | Clinical examination every 3–6 months | | Malignancy screening | Annual examination; biopsy any suspicious lesions | | Adherence | Counsel on Koebner phenomenon; avoid trauma | **Mnemonic: "STOP LP"** — Steroids (topical first), Topical agents, Observe (monitor), Proceed to systemic if needed; Lesions (monitor for malignancy), Protect from trauma [cite:Robbins 10e Ch 25; Harrison 21e Ch 325]