What is lichen planus?
Lichen planus is a chronic inflammatory skin condition affecting skin and/or mucosal surfaces. There are several clinical types of lichen planus that share similar features on histopathology.
- Cutaneous lichen planus
- Mucosal lichen planus
- Lichen planopilaris
- Lichen planus of the nails
- Lichen planus pigmentosus
- Lichenoid drug eruption
Who gets lichen planus?
Lichen planus affects about one in one hundred people worldwide, mostly affecting adults over the age of 40 years. About half those affected have oral lichen planus, which is more common in women than in men. About 10% have lichen planus of the nails.
What causes lichen planus?
Lichen planus is a T cell-mediated autoimmune disease, in which inflammatory cells attack an unknown protein within 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—isomorphic response (koebnerisation)
- Localised skin disease such as herpes zoster—isotopic response
- 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)
- Drugs; gold, quinine, quinidine and others can cause a lichenoid rash
A lichenoid inflammation is also notable in graft-versus-host disease, a complication of bone marrow transplant.
What are the clinical features of lichen planus?
Lichen planus may cause a small number or many lesions on the skin and/or 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 scaly.
- Bullous lichen planus is rare.
- 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.
Cutaneous lichen planus
Oral lichen planus
The mouth is often the only affected area. Oral lichen planus often involves the inside of the cheeks and the sides of the tongue, but the gums and lips may also be involved. The most common patterns are:
- Painless white streaks in a lacy or fern-like pattern
- Painful and persistent erosions and ulcers (erosive lichen planus)
- Diffuse redness and peeling of the gums (desquamative gingivitis)
- Localised inflammation of the gums adjacent to amalgam fillings
Vulval lichen planus
Lichen planus may affect labia majora, labia minora and vaginal introitus. Presentation includes:
- Painless white streaks in a lacy or fern-like pattern
- Painful and persistent erosions and ulcers (erosive lichen planus )
- Scarring, resulting in adhesions, resorption of labia minora and introital stenosis
- Painful desquamative vaginitis, preventing intercourse, and causing a mucky discharge. The eroded vagina may bleed easily on contact
- Overlap with vulval lichen sclerosus, an inflammatory skin disorder that most commonly affects women over 50 years of age.
Penile lichen planus
Penile lichen planus usually presents with classical papules in a ring around the glans. White streaks and erosive lichen planus may occur but are less common.
Other mucosal sites
Erosive lichen planus uncommonly affects the lacrimal glands, eyelids, external ear canal, oesophagus, larynx, bladder and anus.
Lichen planopilaris presents as tiny red spiny follicular papules on the scalp or less often, elsewhere on the body. Rarely, blistering occurs in the lesions. Destruction of the hair follicles leads to permanently bald patches characterised by sparse “lonely hairs”.
Frontal fibrosing alopecia is a form of lichen planopilaris that affects the anterior scalp, forehead and eyebrows.
Pseudopelade of Brocq is probably a variant of lichen planus without inflammation or scaling. Areas of scarring without hair slowly appear, described as “like footprints in the snow”.
Nail lichen planus
Lichen planus affects one or more nails, sometimes without involving the skin surface. It is called twenty-nail dystrophy if all nails are abnormal and nowhere else is affected. Lichen planus thins the nail plate, which may become grooved and ridged. The nail may darken, thicken or lift off the nail bed (onycholysis). Sometimes the cuticle is destroyed and forms a scar (pterygium). The nails may shed or stop growing altogether, and they may rarely, completely disappear (anonychia).
Lichen planus of nails
Lichen planus pigmentosus
Lichen planus pigmentosus describes ill-defined oval, greyish brown marks on the face and neck or trunk and limbs without an inflammatory phase. It can be provoked by sun exposure but can also arise in sun-protected sites such as the armpits. It has diffuse, reticulate and diffuse patterns. Lichen planus pigmentosus is similar to erythema dyschromicum perstans and may be the same disease.
Lichen planus pigmentosus may rarely affect the lips, resulting in a patchy dark pigmentation on upper and lower lips.
Lichenoid drug eruption
Lichenoid drug eruption refers to a lichen planus-like rash caused by medications. Asymptomatic or itchy; pink, brown or purple; flat, slightly scaly patches most often arise on the trunk. The oral mucosa (oral lichenoid reaction) and other sites are also sometimes affected. Many drugs can rarely cause lichenoid eruptions. The most common are:
Quinine and thiazide diuretics cause photosensitive lichenoid drug eruption.
Complications of lichen planus
Rarely, longstanding erosive lichen planus can result in squamous cell carcinoma (squamous cell carcinoma) of the mouth (oral cancer), vulva (vulval cancer) or penis (penile cancer). This should be suspected if there is an enlarging nodule or an ulcer with thickened edges. Cancer is more common in smokers, those with a past history of cancer in mucosal sites, and in those who carry oncogenic human papillomavirus.
Cancer from other forms of lichen planus is rare.
How is lichen planus diagnosed?
In most cases, lichen planus is diagnosed by observing its clinical features. A biopsy is often recommended to confirm or make the diagnosis and to look for cancer. The histopathological signs are of a lichenoid tissue reaction affecting the epidermis.
Typical features include:
- Irregularly thickened epidermis
- Degenerative skin cells
- Liquefaction degeneration of the basal layer of the epidermis
- Band of inflammatory cells just beneath the epidermis
- Melanin (pigment) beneath the epidermis
Direct staining by immunofluorescent techniques may reveal deposits of immunoglobulins at the base of the epidermis.
Patch tests may be recommended for patients with oral lichen planus affecting the gums, to assess for contact allergy to mercury.
What is the treatment for lichen planus?
Treatment is not always necessary. Local treatments for symptomatic cutaneous or mucosal disease are:
- Potent topical steroids
- Topical calcineurin inhibitors, tacrolimus ointment and pimecrolimus cream
- Topical retinoids
- Intralesional steroid injections
Systemic treatment for widespread or severe local disease often includes a 1–3 month course of oral prednisone, while commencing another agent from the following list:
In cases of oral lichen planus affecting the gums with contact allergy to mercury, the lichen planus may resolve on replacing the fillings with composite material. If the lichen planus is not due to mercury allergy, removing amalgam fillings is very unlikely to result in cure.
What is the outlook for lichen planus?
Cutaneous lichen planus tends to clear within a couple of years in most people, but mucosal lichen planus is more likely to persist for a decade or longer. Spontaneous recovery is unpredictable, and lichen planus may recur at a later date. Scarring is permanent, including balding of the scalp.
Lichenoid drug eruptions clear up slowly when the responsible medication is withdrawn.