Lichen planus (LP) is a chronic inflammatory and immune-mediated disease that affects the skin, nails, hair, and mucous membranes. 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. Although there is a broad clinical range of LP manifestations, the skin and oral cavity remain as the major sites of involvement.
Oral LP is considered to be a T-cell mediated chronic inflammatory tissue reaction that results in a cytotoxic reaction against epithelial basal cells. The inflammatory infiltrate in oral LP is primarily composed of CD8+ T cells. A potential pathway for CD8+ T cell-mediated cytotoxicity in oral LP is described as follows:
Antigens presented on MHC 1 molecules activates CD8+ T cells on keratinocytes or by encounters with activated CD4+ helper T cells or cytokines produced by activated CD4+ helper T cells
Activated CD8+ T cells induce keratinocyte apoptosis through various mechanisms such as secretion of tumor necrosis factor (TNF)-alpha, secretion of granzyme B, or Fas-Fas ligand interactions. Chemokines are produced by activated CD8+ T cells that attract additional inflammatory cells, thereby promoting continued inflammation.
Other mechanisms that have been proposed include:
Upregulation of matrix metalloproteinases that disrupt the epithelial basement membrane zone and allow entry of immune cells into the epidermis,
the release of proinflammatory mediators and proteases by mast cells, and
perturbations in the innate immune response that may involve toll-like receptors.
There is no cure for lichen planus, and so treatment of cutaneous and oral lichen planus is for symptomatic relief or due to cosmetic concerns. When medical treatment is pursued, first-line treatment typically involves either topical or systemic corticosteroids, and removal of any triggers. Without treatment, most lesions will spontaneously resolve within 6–9 months for cutaneous lesions, and longer for mucosal lesions.
Many different treatments have been reported for cutaneous lichen planus, however there is a general lack of evidence of efficacy for any treatment. Treatments tend to be prolonged, partially effective and disappointing. The mainstay of localized skin lesions is topical steroids. Additional treatments include retinoids, such as acitretin, or sulfasalazine. Narrow band UVB phototherapy or systemic PUVA therapy are known treatment modalities for generalized disease.
Reassurance that the condition is benign, elimination of precipitating factors and improving oral hygiene are considered initial management for symptomatic OLP, and these measures are reported to be useful.
Treatment usually involves topical corticosteroid (such as betamethasone, clobetasol, dexamethasone, and triamcinolone) and analgesics, or if these are ineffective and the condition is severe, then systemic corticosteroids may be used. Calcineurin inhibitors (such as pimecrolimus, tacrolimus or cyclosporin) are sometimes used. While topical steroids are widely accepted as first line treatment for mucosal lichen planus, there is only weak evidence to support their effectiveness for erosive oral lichen planus.
Cutaneous lichen planus lesions typically resolve within 6 months to a year. However, some variant such as the hypertrophic variant might persist for years if left untreated or unmonitored.
It is found that cutaneous lichen planus does not carry a risk of skin cancer. In contrast to cutaneous LP, which is self limited, lichen planus lesions in the mouth may persist for many years, and tend to be difficult to treat, with relapses being common.
It is found that patients with erythematous or erosive oral lichen planus have a higher risk of oral squamous cell carcinoma compared to patients diagnosed with other variants.
Due to the possibility that oral LP may increase risk for oral cancer, patients with oral lichen planus are encouraged to avoid activities known to increase the risk for oral cancer, such as smoking and alcohol use.
Patient with oral lichen planus should be followed-up at least every 6 to 12 months, to assess the disease activity, changes in symptoms or even detect early signs of malignancy.
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