Lichen planus is an uncommon skin condition whose cause is unknown.

It is thought to be due to an abnormal immune reaction, possibly started by a viral infection. Inflammatory cells seem to mistake the skin cells as foreign and attack them. Your doctor may recommend testing to check for any underlying infection.

Lichen planus occurs worldwide.

Often the onset of lichen planus is slow, taking months to reach its peak. It usually clears within 18 months but in a few people persists for many years.

A similar condition, called a lichenoid drug eruption, is sometimes caused by medications such as gold given for arthritis, antimalarial tablets and captopril (a medicine for high blood pressure). Lichenoid drug eruptions clear up slowly when the responsible medication is withdrawn.

The skin rash is characterized by shiny flat-topped papules (bumps) on the skin varying from pinpoint size to larger than a centimeter. They are a purple color and often are crossed by fine white lines (Wickham's striae). They may be close together or widespread, or grouped in lines or rings. They are often very itchy.

As the lichen planus papules clear they are often replaced by areas of brown discoloration, especially in darker skinned people. New lesions may appear while others are clearing. Some may become thick and scaly. If the hair follicles are involved, tiny spiny papules are seen. Rarely, blistering occurs in the lesions.

Lichen planus may affect any area, but is most often seen on the front of the wrists, lower back, and ankles. On the palms and soles, the papules are firm and yellow.

In 50% of cases the mouth is involved with painless white streaks, and sometimes painful ulcers (erosive lichen planus). The usual areas affected are the inside of the cheeks and the tongue. This is known as oral lichen planus.

In women, a similar condition rarely affects the vulva (erosive vulvitis) and can extend to involve the vagina (desquamative vaginitis). This may be an extremely painful and distressing condition.

The scalp is uncommonly affected, but permanent bald patches may develop (lichen planopilaris). In 10% of cases there is nail involvement, usually a minor change but occasionally resulting in shedding or destruction of the nail.

Treatment

Treatment is not always necessary.

Potent and ultrapotent topical steroids

Topical steroids such as clobetasol proprionate and betamethasone propionate ointments are generally applied for 4 -6 weeks. A thin smear should be rubbed in twice a day and stopped when the lesions have flattened with the normal skin. Brown marks are often left at the sites, which may take several months to fade.

Systemic steroids

In extensive cases systemic steroids such as prednisone may be prescribed for a few weeks or longer. This will lessen the itch and often clear up the lichen planus completely. However, it may recur later. Systemic steroids may have serious side effects, so discuss this treatment with your dermatologist.

Other treatments include long term antibiotics, oral antifungal agents, phototherapy, acitretin, hydroxychloroquine, and tacrolimus.