Aetiology

There are no proven causes, but it is thought that autoimmunity is involved. Hepatitis C may also induce susceptibility by changing cytokine expression in some patient populations.[30] Oral allergens may play a role in oral disease, and meta-analysis suggests a high prevalence of thyroid disease among patients with oral LP.[31][32]​ Exogenous antigens, such as those found in tattoo ink, may encourage development at tattoo sites.[33]​ Certain drugs and vaccines have also been associated with LP.[16][17][18]​​[34]

Pathophysiology

Activated T-lymphocytes migrate to dermal-epidermal junctions and induce apoptosis of basal keratinocytes.[1] Although both CD4+ and CD8+ T-lymphocytes are present, the latter predominate in older lesions.[1] It is thought that increased expression of ICAM-1 and Th1 cytokines (including interferon-gamma, TNF-alpha and nuclear factor kappa B [NF-KB] -dependent cytokines) promote apoptosis.[35][36][37][38][39][40][41] Other evidence indicates that neoangiogenesis is an important pathophysiological factor.[41]

Classification

Lesion site

Cutaneous [Figure caption and citation for the preceding image starts]: Cutaneous lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@50fcdcc1[Figure caption and citation for the preceding image starts]: Blaschkoid lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@46ad5d32[Figure caption and citation for the preceding image starts]: Blaschkoid lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@5e70b213[Figure caption and citation for the preceding image starts]: Inverse lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@6eddcbb7[Figure caption and citation for the preceding image starts]: Hypertrophic lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@70855010[Figure caption and citation for the preceding image starts]: Hypertrophic lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@412330fc

  • Classically presents with itchy, violaceous, polygonal papules and plaques over the flexor forearms and shins, although other morphologies may be present.[1][2]

Oral [Figure caption and citation for the preceding image starts]: Oral lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@2e4e11a1

  • May present with asymptomatic or uncomfortable white, net-like patches or with painful erosions and ulceration.[3]

Genital mucosal [Figure caption and citation for the preceding image starts]: Genital lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@57386bc1

  • May be associated with pain or pruritus.[4]

Lichen planopilaris [Figure caption and citation for the preceding image starts]: Lichen planopilarisMayo Clinic clinical photographs (used with permission). [Citation ends].com.bmj.content.model.Caption@4f9c53f3

  • Affects the scalp and often results in scarring alopecia.[5][6]

Ungual [Figure caption and citation for the preceding image starts]: Ungual lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@73fb97da[Figure caption and citation for the preceding image starts]: Ungual lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@5e66e915

  • Can cause dorsal pterygium, longitudinal ridging, nail-plate thinning, and distal splitting.[7]

Oesophageal

  • Rare, can cause dysphagia or odynophagia.[8]

Cutaneous lesion configuration

Blaschkoid [Figure caption and citation for the preceding image starts]: Blaschkoid lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@77f35ad4[Figure caption and citation for the preceding image starts]: Blaschkoid lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@317c0963

  • Lesions following the lines of Blaschko.[9][10][11]

Zosteriform [Figure caption and citation for the preceding image starts]: Zosteriform lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@3fd97aa

  • Lesions following dermatomal lines.[12]

Linear

  • Lesions arranged in linear distributions.[1][2]

Inverse [Figure caption and citation for the preceding image starts]: Inverse lichen planusMayo Clinic clinical photographs (used with permission) [Citation ends].com.bmj.content.model.Caption@4a35571a

  • Lesions present in intertriginous areas, such as the groins and axillae. Scale may be absent.[1][2][13]

Cutaneous lesion morphology

Hyper-trophic

  • Hyper-keratotic nodules, most commonly distributed on the distal lower extremities.[1][2]

Bullous

  • Polygonal papules with associated vesicles or bullae.[1][2]

Actinic

  • Lesions present in photodistributions (at sites routinely exposed to the sun).[1][2]

Annular

  • Lesions in annular configurations.[14]

Atrophic

  • Atrophic patches that may or may not be associated with hyper-pigmentation.[15]

Erosive

  • Cutaneous or mucosal erosions or ulcerations.[1][2]

Pigmented

  • Lesions with associated hyper-pigmentation.[13][15]

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