Lichen planus (LP) is a chronic inflammatory and immune mediated disease that affects the skin, nails, hair, and mucous membranes. It is not an actual lichen, but is named for its appearance. It is characterized by polygonal, flat-topped, violaceous papules and plaques with overlying, reticulated, fine white scale (Wickham's striae), commonly affecting dorsal hands, flexural wrists and forearms, trunk, anterior lower legs, and oral mucosa. The hue may be gray-brown in people with darker skin. Although there is a broad clinical range of LP manifestations, the skin and oral cavity remain the major sites of involvement. The cause is unknown, but it is thought to be the result of an autoimmune process with an unknown initial trigger. There is no cure, but many medications and procedures have been used in efforts to control the symptoms. The term lichenoid reaction (lichenoid eruption or lichenoid lesion) refers to a lesion of similar or identical histopathologic and clinical appearance to lichen planus (i.e., an area which resembles lichen planus, both to the naked eye and under a microscope). Sometimes dental materials or certain medications can cause lichenoid reactions. They can also occur in association with graft versus host disease.
Classification Lichen planus lesions are so called because of their "lichen-like" appearance and can be classified by the site they involve, or by their morphology.
Site Lichen planus may be categorized as affecting mucosal or cutaneous surfaces.
Cutaneous forms are those affecting the skin, scalp, and nails. Mucosal forms are those affecting the lining of the gastrointestinal tract (mouth, pharynx, esophagus, stomach, anus), larynx, and other mucosal surfaces including the genitals, peritoneum, ears, nose, bladder and conjunctiva of the eyes.
Pattern Lichen planus lesions can occur in many different forms or morphologies:
Papular Papular form is the classic cutaneous lichen planus (CLP) lesion characterized by shiny, red or purple-colored, flat-topped papule. Lesions may have a thin, transparent, and adherent scale. Fine whitish points or lacy lines (Wickham's striae) may be seen on the surface of well-developed papules. Annular 'Ring-shaped' lesions that develop gradually from single small pigmented spots into circular groups of papules with clear, unaffected skin in the center. The ring-like lesions may very slowly enlarge, coalesce, and morph into larger irregular (serpentine) bands, sometimes accompanied by lines (See Linear, below). Annular CLP is uncommon and classically involves the male genitalia (glans penis and penile shaft), groin, axilla, and also the extremities. Linear Papules are arranged in a line (the "Blaschko line"). This pattern may develop secondary to trauma (koebnerization) or, uncommonly, as a spontaneous, isolated eruption, usually on the extremities, and rarely on the face. Hypertrophic This pattern is characterized by hyperkeratotic thick pruritic red-brown to purple-gray plaques with follicular accentuation. Hypertrophic CLP commonly involves the extremities, especially the interphalangeal joints and the anterior legs in a symmetrical distribution. This form is also known as "lichen planus verrucosus". Atrophic This morphology is characterized by the presence of a few well-demarcated, white-bluish papules or plaques with central superficial atrophy. Atrophic CLP is the clinical endpoint of chronic annular or hypertrophic LP with atrophic lesions. The use of potent topical corticosteroids for a long time may predispose the patient to the development of atrophic lesions. Bullous This morphology is characterized by the development of vesicles and bullae with the skin lesions. This is a rare variant of lichen planus, also known as "vesiculobullous lichen planus". Actinic time Rare form presenting as nummular patches or plaques with a hypopigmented halo surrounding a hyperpigmented center. Actinic CLP is more prevalent in African Americans, Indians, and Middle Eastern individuals and commonly affects the sun-exposed areas. Ulcerative This morphology is characterized by chronic, painful bullae and ulceration of the feet, often with cicatricial sequelae evident. This is a rare variant of lichen planus. Pigmented This morphology is characterized by hyperpigmented, dark-brown macules in sun-exposed areas and flexural folds. This is a rare variant of lichen planus. Follicular Characterized by follicular, flat, elevated, or hemispherical erythematous papules with or without keratoses, presenting in groups or disseminated. The Graham‐Little‐Piccardi‐Lasseur syndrome, seen in a familial pattern and also predominantly in women, is characterized by the appearance of follicular LP on the trunk with LP follicularis decalvans on the scalp. Follicular LP on the scalp is more likely to lead to scarring alopecia. Inverse Characterized by extensive erythematous lesions with poorly defined borders and, in part, with lichenification. Inverse LP typically affects the axillae, inguinal creases, limb flexures, and submammary region. Pigmentation of the individual lesions at these inverse locations is typical. Additionally, keratotic papules and bizarre erosions can occur.
Overlap syndromes Occasionally, lichen planus occurs with other conditions. For example:
Lupus erythematosus overlap syndrome. Lesions of this syndrome share features of both lupus erythematosus and lichen planus. Lesions are usually large, hypopigmented, atrophic, and have a red to blue colour with minimal scaling. Telangectasia may be present. Lichen sclerosus overlap syndrome, sharing features of lichen planus and lichen sclerosus.
Signs and symptoms
Although lichen planus can present with a variety of lesions, the most common presentation is as a well-defined area of purple-coloured, itchy, flat-topped papules with interspersed lacy white lines (Wickham's striae). This description is known as the characteristic "6 Ps" of lichen planus: planar (flat-topped), purple, polygonal, pruritic, papules, and plaques. This rash, after regressing, is likely to leave an area of hyperpigmentation that slowly fades. That said, a variety of other lesions can also occur.
Skin
Variants of cutaneous lichen planus are distinguished based upon the appearance of the lesions and/or their distribution. Lesions can affect the:
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