Lichen planus


Lichen planus is a chronic inflammatory and autoimmune 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, 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 as 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 different medications and procedures have been used in efforts to control the symptoms.
The term lichenoid reaction refers to a lesion of similar or identical histopathologic and clinical appearance to lichen planus. 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.
Lichen planus lesions can occur in many different forms or morphologies:
;Papular
;Annular
;Linear
; Hypertrophic
; Atrophic
; Bullous
; Actinic
; Ulcerative
; Pigmented
; Follicular
; Inverse

Overlap syndromes

Occasionally, lichen planus is known to occur 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 and hypopigmented, atrophic, and with a red to blue colour and 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. This description is known as the characteristic "6 Ps" of lichen planus: planar, 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:
  • Extremities. This is more common in Middle Eastern countries in spring and summer, where sunlight appears to have a precipitating effect.
  • Palms and soles
  • Intertriginous areas of the skin. This is also known as "inverse lichen planus".
  • Nails characterized by irregular longitudinal grooving and ridging of the nail plate, thinning of the nail plate, pterygium formation, shedding of the nail plate with atrophy of the nail bed, subungual keratosis, longitudinal erthronychia, and subungual hyperpigmentation. A sand-papered appearance is present in around 10% of individuals with nail lichen planus.
  • Hair and scalp. The scalp is rarely affected by a condition known as lichen planopilaris, acuminatus, follicular lichen planus, and peripilaris, characterised by violaceous, adherent follicular scale with progressive scarring alopecia. While lichen planus and lichen planopilaris may occur together, aside from sharing the term 'lichen' and revealing inflammation on skin biopsy, there is neither established data on their co-occurrence nor data to suggest a common etiology. Lichen planopilaris is considered an orphan disease with no definitive prevalence data and no proven effective treatments.
Other variants may include:
  • Lichen planus pemphigoides characterized by the development of tense blisters atop lesions of lichen planus or the development vesicles de novo on uninvolved skin.
  • Keratosis lichenoides chronica is a rare dermatosis characterized by violaceous papular and nodular lesions, often arranged in a linear or reticulate pattern on the dorsal hands and feet, extremities, and buttock, and some cases manifest by seborrheic dermatitis-like eruption on the scalp and face; also palmo plantar keratosis has been reported.
  • Lichenoid keratoses is a cutaneous condition characterized by brown to red scaling maculopapules, found on sun-exposed skin of extremities. Restated, this is a cutaneous condition usually characterized by a solitary dusky-red to violaceous papular skin lesion.
  • Lichenoid dermatitis represents a wide range of cutaneous disorders characterized by lichen planus-like skin lesions.

    Mucous membranes

Lichen planus affecting mucosal surfaces may have one lesion or be multifocal. Examples of lichen planus affecting mucosal surfaces include:
Oral lichen planus, is a form of mucosal lichen planus, where lichen planus involves the oral mucosa, the lining of the mouth. This may occur in combination with other variants of lichen planus. Six clinical forms of oral lichen planus are recognized:
; Reticular
; Erosive or ulcerative
; Papular
; Plaque-like
; Atrophic
; Bullous
These types often coexist in the same individual. Oral lichen planus tends to present bilaterally as mostly white lesions on the inner cheek, although any mucosal site in the mouth may be involved. Other sites, in decreasing order of frequency, may include the tongue, lips, gingivae, floor of the mouth, and very rarely, the palate.
The most common symptoms of OLP include pain, burning, and discomfort in affected areas of the mouth. In severe cases, OLP is associated with debilitating pain causing difficulty speaking, eating, and swallowing, which may result in malnutrition and weight loss, or compromising airways and leading to breathing difficulties. In addition to physical discomfort, OLP can cause anxiety, depression, social isolation, and compromised quality of life, impacting patients' ability to work and participate in social life. Generally, OLP tends not to cause any discomfort or pain in mild cases, although many people experience significant soreness when eating or drinking acidic or spicy foodstuffs or beverages.
Oral lichen planus represents a serious chronic condition with significant unmet medical need. The FDA has recognized OLP as a serious disease warranting expanded access programs for investigational treatments, acknowledging the substantial impact on patients' daily functioning and quality of life. When symptoms arise, they are most commonly associated with the atrophic and ulcerative subtypes. These symptoms can include a burning sensation to severe pain. They may also experience mucosal bleeding in response to mild trauma, such as toothbrushing. Additionally, the Koebner phenomenon is not only present in cutaneous lichen planus but can also occur in the setting of OLP.
Severe manifestations of OLP include:
• Pain that interferes with basic oral functions including speaking, eating, and swallowing
• Malnutrition and weight loss due to difficulty eating
• Respiratory compromise when lesions affect airway passages
• Psychological impact including anxiety, depression, and social isolation
• Impaired work performance and reduced ability to participate in social activities
• Oral hygiene deficits due to pain during tooth brushing or denture wear
The disease affects approximately 6 million Americans with currently no FDA-approved therapies available, highlighting the substantial unmet medical need in this patient population.
Residual postinflammatory hyperpigmentation has been reported in association with OLP, manifesting as brown to black pigmentation on the oral mucosa and may most likely occur in dark-skinned individuals.
OLP may occur as a sole manifestation of the disease or in conjunction with other clinical manifestations of LP, including cutaneous LP, genital LP, nail LP, and lichen planopilaris.

Causes

Cutaneous LP is a self-limiting condition. It usually resolves within 6 to 12 months. Oral LP is a non infectious, chronic inflammatory condition that involves the oral mucosa and may be accompanied by skin lesions. The etiology of oral LP are unknown.
It is not clear whether the mechanisms causing isolated oral LP are different from those causing oral LP with cutaneous LP. An immune-mediated mechanism where basal keratinocytes are being targeted as foreign antigens by activated T cells, especially CD8+ T cells, has been proposed. Upregulation of intercellular adhesion molecule-1 and cytokines associated with T-helper 1 immune response, may also play an important role in the pathogenesis of lichen planus.
Stress is thought to play a role in the pathogenesis of oral LP. Patients with anxiety and depression are reported more commonly with oral LP if compared to normal healthy individuals. Some studies have indicated that stressful events can induce LP lesions in otherwise healthy individuals. However, a cause effect relationship between stress and the onset of oral LP has not been demonstrated.
Autoimmune response to epithelial self-antigens remains a possibility. A single study of cutaneous LP reported evidence in support of autoimmunity by expanding in vitro T cells isolated from the skin lesions of two patients, followed by testing the ability of these T cells to kill autologous keratinocytes.
Several potential triggers of oral LP have been proposed over the years, mainly
  1. Hypersensitivity reaction
  2. * Restorative material or drugs can cause hypersensitivity reaction and lead to oral LP.
  3. * Oral LP usually resolve upon removal of the trigger, as is characteristics of oral LP
  4. Viral infection