Key Facts

Lichen planus is a common inflammatory dermatosis that can affect the skin, oral mucosa, genital mucosa, nails, and scalp. It is important because of its association with hepatitis C and the premalignant potential of erosive oral lichen planus.

Epidemiology

• Prevalence: ~0.5–1% of population
• Peak age: 30–60 years
• M:F ~equal for cutaneous; F > M for oral LP
• Oral LP: 1–2% prevalence in adults

Aetiology

• T-cell mediated autoimmune: CD8+ cytotoxic T-cells attack basal keratinocytes
• Hepatitis C: significant association (particularly oral LP); screen all patients
• Drug-induced lichenoid eruption: beta-blockers, NSAIDs, ACE inhibitors, antimalarials, thiazides, gold
• Dental amalgam: lichenoid contact reaction
• Graft-versus-host disease: lichenoid features common

Pathophysiology

• Cytotoxic T-lymphocytes target basal keratinocyte antigens → apoptosis of basal cells (civatte/colloid bodies)
• Band-like (lichenoid) lymphocytic infiltrate at dermal-epidermal junction
• Disruption of basement membrane → pigment incontinence (post-inflammatory hyperpigmentation)
• 'Saw-tooth' irregular acanthosis of rete ridges on histology

Cutaneous Lichen Planus

• 5 Ps: Pruritic, Polygonal, Purple/violaceous, Planar (flat-topped), Papules
• 2–10 mm diameter; shiny surface
• Wickham's striae: white lacy lines on papule surface
• Distribution: flexor surfaces (wrists, forearms), shins, lower back
• Koebner phenomenon: new lesions at sites of trauma
• Resolves with post-inflammatory hyperpigmentation

Oral Lichen Planus

• Reticular: white lacy pattern (Wickham's striae) on buccal mucosa — most common; usually asymptomatic
• Erosive: painful erythematous erosions/ulcers — may affect eating; premalignant (~1% risk of oral SCC)
• Atrophic: red, glazed areas
• Bilateral buccal mucosa involvement is characteristic

Other Sites

• Genital LP: vulval/penile erosions — painful, may cause scarring
• Nail LP: thinning, longitudinal ridging, pterygium (scarring of nail fold)
• Scalp (lichen planopilaris): scarring alopecia — irreversible hair loss

Red Flags

• Erosive oral LP: premalignant — requires long-term monitoring
• Scarring alopecia (lichen planopilaris) — irreversible
• Oesophageal LP: dysphagia — rare
• Drug-induced: review medication list

Bedside

• Clinical examination: characteristic morphology, Wickham's striae (use dermoscopy), Koebner phenomenon
• Oral examination: reticular/erosive changes on buccal mucosa
• Genital, nail, and scalp examination

Bloods

• Hepatitis C serology: screen ALL lichen planus patients
• LFTs: hepatitis C association
• FBC, U&Es: baseline if considering systemic treatment

Biopsy

• Punch biopsy: band-like lymphocytic infiltrate at DEJ, 'saw-tooth' rete ridges, civatte bodies (apoptotic keratinocytes), hypergranulosis
• DIF: rarely needed; may show fibrinogen deposition at BMZ (shaggy fibrin)

Special Tests

• Dermoscopy: Wickham's striae appear as white crossing lines
• Oral biopsy: for erosive oral LP — exclude dysplasia/SCC

Non-Pharmacological

• Patient education: usually self-limiting (1–2 years for cutaneous LP)
• Avoid triggers: review medications for lichenoid drug eruptions; dental amalgam consideration
• Oral LP monitoring: 6–12 monthly review for erosive disease (malignant potential)

Pharmacological

Cutaneous LP:

• Potent topical corticosteroids: clobetasol propionate 0.05% or betamethasone valerate 0.1% — first-line
• Topical tacrolimus 0.1% ointment: steroid-sparing alternative
• Oral prednisolone 0.5–1 mg/kg: short course for severe/widespread disease
• Acitretin 25–50 mg OD: for widespread, refractory cutaneous LP
• Phototherapy (narrowband UVB): for widespread disease

Oral LP:

• Topical corticosteroid mouthwash/paste: betamethasone 0.5 mg dissolved in 10 mL water as mouthwash; or clobetasol in adhesive paste
• Topical tacrolimus 0.1%: for erosive oral LP
• Oral prednisolone: short course for severe erosive flares

Lichen planopilaris:

• Potent topical steroids to scalp
• Hydroxychloroquine 200 mg BD: first-line systemic
• Aim to halt progression — scarring alopecia is irreversible

Referral Criteria

• Dermatology: severe/widespread disease, erosive oral LP, lichen planopilaris
• Oral medicine/maxillofacial: erosive oral LP — long-term monitoring
• Hepatology: if hepatitis C positive

• Cutaneous LP: usually self-limiting within 1–2 years; ~20% may recur
• Oral LP: may persist for decades; erosive form requires long-term monitoring
• Erosive oral LP: ~1% risk of progression to oral SCC over 5–10 years
• Lichen planopilaris: scarring alopecia is irreversible — early treatment to halt progression
• Nail LP: may cause permanent nail dystrophy
• Post-inflammatory hyperpigmentation: common, especially in darker skin types; may persist for months–years

Lichen Planus Variants

Lichenoid Drug Reactions — Common Culprits