Lichen planus

Overview

The 6 P's are the core exam target for lichen planus.

•Pruritic - intense itch driven by inflammatory cytokines

•Polygonal - irregular, many-sided shape

•Planar (flat-topped) - band-like infiltrate pressing against epidermis

•Purple/violaceous - dense lymphocytic infiltrate and vascular dilatation

•Papules (or plaques) - solid raised lesions

•Pattern - Wickham's striae: white lacy lines on the surface caused by focal hypergranulosis

•Distribution - flexor aspects of wrists and ankles, lower back, palms, soles, genitalia

•Koebner phenomenon - new lesions appear at sites of skin trauma (scratch, scar, venepuncture)

•Oral involvement (~50%) - white lacy reticular pattern on buccal mucosa; cannot be wiped off (distinguishes from oral candidiasis)

•Other variants - lichen planopilaris (scarring alopecia), nail involvement (longitudinal ridging, pterygium unguis), erosive genital LP

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Oral candidiasis plaques can be wiped off with a spatula; oral LP striae cannot - a classic differentiating point.

Investigations

•Lichen planus is primarily a clinical diagnosis

•Skin biopsy (punch) - saw-tooth epidermal hyperplasia, hypergranulosis, vacuolar degeneration of basal layer, dense band-like lymphocytic infiltrate at dermo-epidermal junction, Civatte bodies

•Hepatitis C serology (HCV antibody) - strongest systemic association; consider LFTs

•Patch testing - if allergic contact dermatitis (e.g. dental amalgam) suspected in oral LP

Management

•If a causative drug is identified (thiazide diuretics, antimalarials, NSAIDs, ACE inhibitors, gold salts), stop it first

•Avoid skin trauma (prevents Koebnerisation); for oral LP avoid alcohol and smoking (SCC risk)

•Symptomatic itch - chlorphenamine (sedating antihistamine), emollients

🥇 First-line

•clobetasol propionate (potent topical corticosteroid) - reduces inflammation; steroid-impregnated tape for localised lesions

•First-line (steroid-sparing / facial, genital, oral): tacrolimus ointment or pimecrolimus cream (calcineurin inhibitors)

•First-line (oral LP): ciclosporin mouthwash or topical steroid rinses

🥈 Second-line

•prednisolone oral (1-3 month course) for widespread/severe disease; hydroxychloroquine for chronic/relapsing disease (requires baseline eye test); acitretin for hypertrophic LP (teratogenic - pregnancy prevention required)

🥉 Third-line

•methotrexate or azathioprine for refractory disease (monitor FBC, LFTs); UVB phototherapy for extensive lower limb LP

Complications

•Squamous cell carcinoma - most important complication; ~1% lifetime risk in oral LP; biopsy any suspicious lesion; regular follow-up essential

•Scarring alopecia - lichen planopilaris; irreversible once established

•Nail destruction - pterygium unguis can cause permanent nail loss

Prognosis

•Cutaneous LP is often self-limiting - resolves within 1-2 years

•Oral and genital forms are more chronic, prone to relapse, and persist for many years

•Post-inflammatory hyperpigmentation is common after resolution, particularly in darker skin types

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Lichen sclerosus (not lichen planus) is the diagnosis in an elderly woman with itchy, white/porcelain atrophic plaques on the vulva or glans penis - it is associated with autoimmune conditions (e.g. type 1 diabetes) and carries an SCC risk. It does not produce Wickham's striae.