Lichen planus (LP) is a pruritic, chronic inflammatory dermatosis resulting from keratinocyte apoptosis that affects the skin, mucous membranes, genitalia, scalp (lichen planopilaris), and nails.

Aetiology: Unknown but a strong association with Hep C

PC

• Pruritis
• Violaceous (purple) flat-topped papules or plaques
  • Lesions are most commonly found on the flexor wrists and ankles but also on the trunk and extremities. May occur on the vulva in genital disease.
• Wikham’s striae - overlying lacy white networks may be seen
• Mucosal erosions and lacy white networks
• Scarring alopecia and nail involvement are uncommon

Management

• 1st line: Topical corticosteroid (clobetasol)
• benzydamine mouthwash or spray is recommended for oral lichen planus
• extensive lichen planus may require oral steroids or immunosuppression

Lichen eruption

Lichen planus is thought to be an autoimmune condition. Where there is an obvious trigger, this is called a lichenoid eruption. A lichenoid eruption is usually caused by medication and presents similarly to lichen planus, although more commonly affects the trunk and Wickham striae are usually absent. Additionally lichenoid eruptions do not usually affect the oral mucosa. Typically a lichenoid eruption occurs 2 months after starting a medication.

Causes