Most common lichenoid disorder; lichenoid disorders are conditions characterised by damage to basal epidermis

Aetiology

• Chronic inflammatory disease of unknown origin
• Recognised triggers include Hepatitis C infection, allergic contact dermatitis, localised skin injury or infection, and certain medications, causing a lichenoid eruption

Clinical features

• Cutaneous lichen planus: characterized by pruritic, polygonal, planar, purple papules or plaques, often with white lacy lines (Wickham's striae) on the surface
  • Lesions typically appear on the flexor aspects of the wrist and ankles, and nail involvement may present as longitudinal ridging
  • Can develop at the site of trauma

• Oral lichen planus: features mucosal ulceration and Wickham's striae in a reticular pattern on the gums and tongue, causing a burning sensation on eating
  • The striae cannot be wiped off, unlike oral candida

Investigations

Usually clinical diagnosis, certain investigations may support the diagnosis:

• Hepatitis C testing: as the condition may be triggered by hepatitis C
• Patch testing: to identify possible contact dermatitis
• Biopsy: can be used to confirm a diagnosis, especially if considering SCC as a differential
  • Irregular sawtooth acanthosis
  • Hypergranuloss and orthohyperkeratosis
  • Band-like upper dermal infiltrate of lymphocytes
  • Basal damage with formation of cytoid bodies

Management

• Conservative measures: avoiding trauma to prevent Koebnerisation, and abstaining from alcohol or smoking due to the elevated risk of oral squamous cell carcinoma
• Anti-histamine: for itch
• Topical therapy: potent corticosteroids, tacrolimus, or ciclosporin mouthwash
• Systemic therapy: steroids, methotrexate, acitretin, or hydroxychloroquine may be utilized.