• Cutaneous lichen planus
• Mucosal lichen planus
• Mucosal lichen planus
• Lichen planus of the nails
• Lichen planus pigmentosus
• Lichenoid drug eruption.

Who gets lichen planus?

Lichen planus affects approximately 1% of the population worldwide, mostly affecting adults aged between 30 to 60 years. It has no strong racial predilection.

Approximately 10% of those affected have lichen planus of the nails while half of those affected have oral lichen planus, which is more common in women than in men.

What causes lichen planus?

Lichen planus is a T-cell mediated autoimmune disorder in which inflammatory cells attack an unknown protein within the skin and mucosal keratinocytes.

Contributing factors to lichen planus may include:

• Genetic predisposition
• Physical and emotional stress
• Injury to the skin; lichen planus often appears where the skin has been scratched or after surgery (koebnerisation)
• Localised skin disease such as herpes zoster
• Systemic viral infection, such as hepatitis C (which might modify self-antigens on the surface of basal keratinocytes)
• Contact allergy, such as to metal fillings in oral lichen planus (rare) and colour photographic developers
• Drugs; gold, quinine, quinidine, and others can cause a lichenoid rash.

Lichenoid inflammation is also notable in graft-versus-host disease.

What are the clinical features of lichen planus?

Lichen planus may cause a small number or many lesions on the skin and mucosal surfaces.

Cutaneous lichen planus

The usual presentation of the disease is classical lichen planus. Symptoms can range from none (uncommon) to intense itch.

• Papules and polygonal plaques are shiny, flat-topped, and firm on palpation.
• The plaques are crossed by fine white lines called Wickham striae.
• Hypertrophic lichen planus can be a scaly and pruritic rash.
• Atrophic lichen planus is a rare annular variant with an atrophic centre.
• Annular lichen planus describes the development of violaceous plaques with central clearing often involving penis, scrotum, and intertriginous areas.
• Size ranges from pinpoint to larger than a centimetre.
• Distribution may be scattered, clustered, linear, annular, or actinic (sun-exposed sites such as face, neck, and backs of the hands)
• Location can be anywhere, but most often front of the wrists, lower back, and ankles.
• Colour depends on the patient’s skin type. New papules and plaques often have a purple or violet hue, except on palms and soles where they are yellowish-brown.
• Plaques resolve after some months to leave greyish-brown post-inflammatory macules that can take a year or longer to fade.