Lichen Planus

What is Lichen Planus?
Pathophysiology: T-Cell Attack on Basal Keratinocytes
Cutaneous Lichen Planus: The 5 P's
Oral and Genital Mucosal Lichen Planus
Clinical Variants: Hair, Nails, and Subtypes
Hepatitis C Association
Drug-Induced Lichenoid Reactions
Diagnosis: Clinical Signs and Histopathology
Malignant Potential of Oral and Vulvar LP
Treatment: Corticosteroids, Retinoids, and Immunosuppressants
Research Papers
Connections
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What is Lichen Planus?

Lichen planus (LP) is a chronic, relapsing, T-cell-mediated inflammatory disease that targets basal keratinocytes — the deepest layer of the epidermis. It can affect the skin, oral and genital mucous membranes, hair follicles (lichen planopilaris), and nails, either individually or in combination. The name comes from the Latin "lichen" (a flat, spreading plant growth) and "planus" (flat) — describing the characteristic flat-topped papules of classic cutaneous LP.

Lichen planus affects approximately 0.5–2% of the population worldwide, with equal sex distribution for cutaneous LP. Oral lichen planus affects women more than men at roughly 2:1. Peak onset is typically between the fourth and sixth decades of life, though LP can occur at any age. It is rare in children.

The etiology remains incompletely understood — lichen planus is called "idiopathic" because no single trigger has been identified for most cases. However, immune-mediated attack on basal keratinocytes is the final common pathway, triggered in susceptible individuals by drugs, infections (notably hepatitis C virus), contact allergens, stress, or unknown factors. Understanding LP matters both for symptom control and because certain subtypes — particularly erosive oral LP and vulvar LP — carry a measurable risk of malignant transformation to squamous cell carcinoma.

Pathophysiology: T-Cell Attack on Basal Keratinocytes

Lichen planus is the prototypical example of a lichenoid tissue reaction — a pattern of immune-mediated basal keratinocyte destruction that can be reproduced by a variety of triggers. The fundamental immunological event is:

T-Cell Infiltration and Basal Cell Targeting

Activated CD4+ and CD8+ T lymphocytes migrate to the skin (or mucous membrane) and accumulate in a dense band immediately below the epidermis, targeting basal keratinocytes. CD8+ cytotoxic T cells in the basal layer directly kill keratinocytes via Fas-FasL interactions, perforin/granzyme-B release, and TNF-α secretion. Basal keratinocytes upregulate ICAM-1 and present self-peptides or altered self-antigens (possibly modified by drugs, viral proteins, or contact allergens) on MHC class I molecules — triggering recognition and CTL-mediated killing.

Simultaneously, CD4+ helper T cells in the upper dermis produce interferon-gamma and TNF-α, amplifying the inflammatory response and sustaining the infiltrate. The result is a characteristic band-like (lichenoid) mononuclear infiltrate hugging the DEJ — the signature of LP on histopathology.

Basal Cell Liquefaction

Killed basal keratinocytes undergo apoptosis, producing Civatte bodies (also called colloid bodies or eosinophilic bodies) — eosinophilic, ovoid apoptotic keratinocytes within or just below the epidermis. This is a diagnostic hallmark on skin biopsy. The destruction of the basal cell layer causes the characteristic histological sawtooth rete ridges — irregular, jagged elongations of the rete ridges that reflect the irregular basal cell destruction and compensatory proliferation pattern.

Melanin Incontinence

Damaged basal keratinocytes release melanin granules into the dermis, where they are engulfed by dermal macrophages (melanophages). This produces the clinically visible post-inflammatory hyperpigmentation — the dark brown or gray discoloration that persists for months to years after LP lesions resolve, particularly on darker skin types. This hyperpigmentation can be more distressing than the original lesions.

Why Certain Sites?

LP has a predilection for specific anatomical sites — wrists, shins, lower back (skin); buccal mucosa, tongue, gingiva (oral); vulva, glans penis (genital). The tissue-specific expression of basal keratinocyte antigens, the local immune microenvironment, and site-specific T-cell trafficking patterns likely explain the anatomical distribution. The Koebner phenomenon (LP developing in skin areas subjected to trauma) implies that localized trauma can trigger or amplify the T-cell response at that site.

Cutaneous Lichen Planus: The 5 P's

The classic cutaneous presentation of lichen planus is memorized by dermatology trainees with the mnemonic of the 5 P's:

Pruritic — the lesions are typically intensely itchy, often disproportionately so relative to their appearance
Polygonal — the papules have an irregular, multi-sided rather than round outline, giving them a characteristic geometric shape when examined closely
Purple (violaceous) — the color ranges from pink to violaceous (blue-purple) to brown on lighter skin tones; on darker skin, lesions may appear hyperpigmented brown or gray rather than purple
Planar (flat-topped) — unlike acne papules or nodules, LP papules have a distinctly flat top; dermoscopy reveals this clearly
Papules — the primary lesion is a small, solid elevation of the skin (1–10 mm); papules can coalesce into plaques

Wickham's Striae

A pathognomonic surface feature of LP papules is Wickham's striae — a network of fine, white, lacy (reticulate) or linear lines visible on the surface of the papule when examined with a magnifying lens or dermoscope (after application of oil or water to the surface). Wickham's striae represent focal thickening of the granular layer of the epidermis (hypergranulosis) directly related to the immune-mediated changes in the epidermis above the lichenoid infiltrate. Their presence on skin papules is highly suggestive of LP.

Distribution of Cutaneous LP

Classic cutaneous LP has a predilection for:

Flexor wrists — the most characteristic site; clusters of violaceous flat-topped papules on the inner wrist and forearm
Shins and ankles — lower legs, where lesions may become hypertrophic (see Variants below)
Lower back and sacral area
Genitals — glans penis, vulva
The face, palms, and soles are typically spared in classic cutaneous LP

Oral and Genital Mucosal Lichen Planus

Oral Lichen Planus

Oral LP (OLP) is common, affecting approximately 1–2% of the general population, and may occur with or without cutaneous LP (many patients have isolated oral involvement). The classic presentation is bilateral white reticular (lacy, web-like) lines on the buccal mucosa — often described as a "fishnet" pattern. These reticular lesions are usually asymptomatic or mildly symptomatic and may be discovered incidentally.

However, OLP exists on a spectrum of severity:

Reticular OLP: White lacy lines on the buccal mucosa (most common form; often asymptomatic; benign course)
Papular OLP: White papules, often on the buccal mucosa or tongue
Plaque OLP: Smooth white plaques resembling leukoplakia (must be biopsied to differentiate)
Erosive/ulcerative OLP: Painful irregular erosions or ulcers with surrounding reticular white lines; this form causes significant functional impairment (eating, speaking), has a chronic relapsing course, and carries malignant potential
Atrophic OLP: Diffuse erythematous (red) areas, particularly on the gingiva ("desquamative gingivitis") — red, friable, easily bleeding gingiva that resembles severe gum disease but is immune-mediated
Bullous/vesicular OLP: Rare; fluid-filled vesicles that rupture quickly leaving erosions

OLP characteristically shows bilateral symmetric involvement of the buccal mucosa (both cheeks affected simultaneously) — asymmetric or unilateral lesions should raise suspicion for alternative diagnoses or malignant transformation.

Genital Lichen Planus

Genital LP is commonly underdiagnosed and can cause significant morbidity:

Vulvar LP: Can manifest as reticular white striae on the labia minora (resembling oral reticular LP), or as erosive LP with painful red erosions of the vaginal introitus, labia, and vaginal mucosa. Erosive vulvar LP causes dyspareunia, dysuria, and vaginal discharge. Long-term scarring can produce architectural changes (loss of the labia minora, vaginal stenosis). Malignant potential to vulvar squamous cell carcinoma (VSCC) is established.
Penile LP: Wickham's striae on the glans penis or ring-shaped (annular) lesions — typically less severe than vulvar LP; erosive penile LP is uncommon

Vulvo-vaginal-gingival syndrome (VVG syndrome) — the triad of erosive LP at all three sites simultaneously — is a well-recognized severe variant requiring aggressive systemic immunosuppression.

Clinical Variants: Hair, Nails, and Subtypes

Lichen Planopilaris (LPP) — Scalp and Hair

When lichen planus targets hair follicles, it causes lichen planopilaris (LPP) — a progressive scarring (cicatricial) alopecia. LPP presents with perifollicular erythema and scaling around hair follicles (follicular hyperkeratosis), follicular plugging, and progressive permanent hair loss as follicles are destroyed by the lichenoid infiltrate. Areas of alopecia show smooth, shiny atrophic skin without follicular openings (follicles permanently destroyed = no regrowth possible). Classic LPP involves the scalp vertex and crown; frontal fibrosing alopecia (FFA) — a variant of LPP — causes progressive frontal hairline recession and eyebrow loss, predominantly in postmenopausal women.

Nail Lichen Planus

LP can affect the nail matrix, nail bed, or both. Changes include:

Longitudinal ridging and grooves (longitudinal striations)
Nail plate thinning and fragility
Onychorrhexis (longitudinal splitting)
Dorsal pterygium (pterygium unguis) — a pathognomonic finding where the nail matrix is destroyed and the proximal nail fold fuses to the nail bed, forming a scar-tissue "wing" that permanently divides the nail. Dorsal pterygium is virtually specific to nail LP and cannot regrow once formed.

Nail LP can progress to permanent nail loss (anonychia) and requires early treatment to prevent irreversible nail matrix destruction.

Hypertrophic LP

Hypertrophic (verrucous) LP occurs predominantly on the shins and ankles — chronic LP lesions subjected to repeated scratching or trauma develop thick, hyperkeratotic, wart-like plaques up to several centimeters. These lesions are intensely pruritic and resistant to treatment; they may persist for decades. Long-standing hypertrophic LP on the shins carries a small but real risk of squamous cell carcinoma development within the plaques.

Other Cutaneous Variants

Annular LP: Ring-shaped lesions with central clearing; common on the glans penis and male genitalia
Linear LP: Lesions in a linear Blaschkoid distribution following lines of Blaschko; may represent somatic mosaicism
Inverse LP: LP in flexural areas (axillae, groin, inframammary folds) rather than extensor surfaces
Vesiculobullous LP: Blister formation within LP papules from severe basal cell destruction; rare
Actinic LP: LP triggered by sun exposure; presents on sun-exposed areas; more common in Middle Eastern and Indian populations; lesions may have a melasma-like pigmentary component

Hepatitis C Association

The association between lichen planus (particularly oral LP) and hepatitis C virus (HCV) infection is one of the most consistent and replicated findings in LP epidemiology. Meta-analyses have found that patients with oral LP have approximately 5–10 times higher odds of HCV infection compared to the general population. The association is strongest in Mediterranean (Italian, Spanish) and Japanese populations; weaker in Northern European populations.

Proposed Mechanisms

Direct viral trigger: HCV proteins may alter self-antigens on basal keratinocytes (particularly in the oral mucosa, which may be exposed to viremia through mucosal lymphoid tissue), triggering cross-reactive T-cell responses that persist as LP
Molecular mimicry: HCV proteins share epitopes with keratinocyte self-proteins, generating T cells that cross-react with both HCV and host basal cells
Immune dysregulation: Chronic HCV infection causes broad immune dysregulation (including Th1/Th17 polarization) that may lower the threshold for autoimmune skin reactions

Clinical Implications

All patients with newly diagnosed oral LP (or extensive cutaneous LP without obvious trigger) should be screened for hepatitis C with anti-HCV antibodies ± HCV RNA. If HCV is identified and the patient is eligible for treatment, direct-acting antiviral (DAA) therapy for HCV can result in improvement or even resolution of LP in some patients — providing both hepatological and dermatological benefit. This is distinct from most other LP cases where no modifiable trigger is found.

Drug-Induced Lichenoid Reactions

Many drugs can cause a lichenoid reaction — a skin eruption that is clinically and histologically indistinguishable from (or closely resembles) idiopathic LP. Drug-induced lichenoid reactions are sometimes called "lichenoid drug eruption" to acknowledge that they may have subtle distinguishing features (more eosinophils on histology, presence of parakeratosis, more widespread distribution, photodistribution).

Major Drug Classes Causing Lichenoid Reactions

Antimalarials: Hydroxychloroquine, chloroquine, quinidine — among the most established causes of lichenoid drug eruptions; photodistributed involvement is a clue
Gold salts: Used historically for rheumatoid arthritis; a classic cause of lichenoid eruptions and also oral LP-like stomatitis
Thiazide diuretics: Hydrochlorothiazide, chlorothiazide; may produce photodistributed lichenoid reactions
ACE inhibitors: Captopril, enalapril — lichenoid reactions; captopril's thiol group may act as a hapten
Beta-blockers: Propranolol, practolol; oral LP-like reactions
Penicillamine: Classic cause of both LP and pemphigus-like reactions
Immune checkpoint inhibitors: PD-1/PD-L1 inhibitors (pembrolizumab, nivolumab) cause lichenoid eruptions as immune-related adverse events; histologically identical to idiopathic LP
Dental amalgam (mercury): Contact lichenoid reactions adjacent to amalgam restorations in the oral cavity — considered a contact hypersensitivity to mercury rather than systemic drug eruption; replacement of amalgam with composite may resolve adjacent oral LP lesions

The interval from drug exposure to lichenoid eruption ranges from weeks to years — a long latency that makes drug causation easy to overlook. Resolution of the eruption weeks to months after drug withdrawal confirms drug causation retrospectively.

Diagnosis: Clinical Signs and Histopathology

Clinical Diagnosis

Classic cutaneous LP on the flexor wrists or shins with the 5 P's features and Wickham's striae visible on dermoscopy can often be diagnosed clinically without biopsy. Similarly, bilateral symmetric reticular white lines on the buccal mucosa are clinically diagnostic of reticular OLP.

However, biopsy is essential when:

The diagnosis is uncertain (plaque LP mimicking leukoplakia; erosive OLP mimicking malignancy)
There is suspicion of malignant transformation (especially in erosive OLP or vulvar LP)
Drug-induced lichenoid reaction needs to be separated from idiopathic LP
Clinical response to treatment is absent (to reconsider diagnosis)

Histopathological Features

Biopsy of an LP papule shows the characteristic lichenoid tissue reaction pattern:

Band-like lymphocytic infiltrate: A dense, well-defined ribbon of lymphocytes and histiocytes immediately below the epidermis (the "lichenoid infiltrate"), hugging the DEJ like a storm cloud beneath the epidermis
Vacuolar degeneration of the basal cell layer: Vacuolization and destruction of the basal keratinocytes (the primary immune target)
Sawtooth rete ridges: Irregular, pointed elongations of the rete ridges — described as "saw-tooth" or "zigzag" in morphology — resulting from basal cell destruction and regenerative acanthosis
Civatte bodies (colloid bodies): Eosinophilic, ovoid apoptotic keratinocytes within or just below the epidermis (at the DEJ or papillary dermis); represent dead basal keratinocytes
Hypergranulosis: Thickening of the granular layer (directly above areas of Wickham's striae)
Melanin incontinence: Free melanin granules and melanophages in the upper dermis

Direct immunofluorescence (DIF) on LP biopsy shows non-specific IgM (and less commonly IgG, IgA, C3) deposits within Civatte bodies — a fibrillar, cytoid body pattern at the DEJ. This DIF pattern is suggestive of LP but not diagnostic or specific (unlike the patterns in pemphigus or bullous pemphigoid). Normal-appearing perilesional skin and linear BMZ deposits (which would indicate BP) are absent in LP.

Malignant Potential of Oral and Vulvar LP

The risk of squamous cell carcinoma (SCC) arising in LP lesions is an important reason for long-term surveillance and aggressive management of erosive forms.

Oral LP — Squamous Cell Carcinoma Risk

The malignant transformation rate for oral LP to oral SCC is approximately 0.5–3% over a lifetime, based on pooled analyses of cohort studies. The risk is not uniform across OLP subtypes:

Erosive/atrophic OLP carries the highest transformation risk
Reticular OLP (the most common form) has a much lower risk, potentially negligible
Carcinoma arising in OLP most commonly involves the tongue, floor of mouth, and buccal mucosa
Warning signs requiring urgent biopsy: development of an indurated area, irregular or raised surface, loss of bilaterality, rapid growth, or change in appearance within a known OLP lesion

The World Health Organization (WHO) classifies OLP as a "potentially malignant oral disorder" — placing it in the same category as leukoplakia and erythroplakia as conditions that require ongoing surveillance. Regular 6–12 month reviews by an oral medicine specialist or oral surgeon are recommended for all patients with OLP, not only erosive forms.

Vulvar LP — VSCC Risk

Erosive vulvar LP is increasingly recognized as a precursor to vulvar squamous cell carcinoma (VSCC) through a HPV-independent pathway. Unlike the more common HPV-related VSCC (which arises from vulvar intraepithelial neoplasia), LP-associated VSCC arises from differentiated VIN (dVIN) in the context of chronic inflammatory atypia. The lifetime transformation risk for vulvar LP is estimated at approximately 2–5%, with significant uncertainty given the rarity of long-term prospective data. Women with erosive vulvar LP require regular gynecological examination with a low threshold for biopsy of new, indurated, or persistently non-healing erosions.

Treatment: Corticosteroids, Retinoids, and Immunosuppressants

First-Line: Topical Corticosteroids

High-potency topical corticosteroids are the cornerstone of LP treatment for both cutaneous and mucosal forms:

Cutaneous LP: Clobetasol propionate 0.05% cream or ointment applied to affected skin twice daily. For hypertrophic lesions, occlusion under plastic wrap enhances penetration. Typically applied for 2–4 weeks, then tapered or used intermittently.
Oral LP: Clobetasol 0.05% gel applied directly to oral lesions 2–3 times daily; triamcinolone acetonide in orabase (a bioadhesive paste) for smaller discrete lesions. Systemic absorption from oral mucosal application is limited but patients should avoid swallowing the gel.
Vulvar LP: Clobetasol 0.05% ointment applied to the affected area; maintenance therapy with weaker topical steroids to prevent architectural scarring progression.

Intralesional Corticosteroids

Intralesional triamcinolone acetonide (5–10 mg/mL) injected directly into resistant skin plaques (particularly hypertrophic LP on the shins) or into oral LP lesions can achieve local disease control when topical therapy fails. Intralesional injection for nail LP (targeting the nail matrix) may prevent progression to dorsal pterygium formation.

Topical Calcineurin Inhibitors

Tacrolimus 0.1% ointment and pimecrolimus 1% cream are effective steroid-sparing alternatives, particularly for mucosal LP:

Tacrolimus 0.1% ointment is particularly useful for erosive OLP and erosive vulvar LP — well-tolerated on mucosal surfaces, without the atrophogenic risk of long-term topical steroid use
Also useful for facial LP and intertriginous areas where prolonged high-potency steroid use causes skin atrophy
Note: A black box warning exists regarding theoretical malignant transformation risk with calcineurin inhibitors in areas already at risk for LP-associated SCC — the clinical significance remains debated

Systemic Therapy for Extensive or Refractory LP

Oral corticosteroids (prednisone): For rapidly spreading, generalized, or severely symptomatic cutaneous LP, a short course of prednisone (0.5–1 mg/kg/day tapered over 4–6 weeks) can induce remission. Not suitable for long-term use given side effects.
Acitretin (oral retinoid): Indicated for extensive cutaneous LP unresponsive to topical therapy and for mucosal LP. Acitretin modulates keratinocyte differentiation and has anti-inflammatory effects on the lichenoid infiltrate. Typical dose 25–50 mg/day. Main limitations: teratogenicity (strict pregnancy prevention required; 3-year washout after stopping), mucocutaneous dryness, hypertriglyceridemia. Effective particularly for hypertrophic LP and lichen planopilaris.
Cyclosporine: For severe, refractory, erosive oral LP unresponsive to topical therapy; cyclosporine oral rinse (can be used topically in the mouth) has also been used for OLP. Systemic cyclosporine (2.5–5 mg/kg/day) is reserved for the most severe refractory cases given nephrotoxicity and hypertension risk.
Narrowband UVB (NB-UVB) phototherapy: Effective for generalized cutaneous LP; 2–3 sessions per week for 2–3 months. Not appropriate for mucosal LP.
Hydroxychloroquine: For actinic LP and some cases of oral LP; paradoxically, antimalarials can also cause lichenoid reactions, requiring careful consideration in individual cases.
Mycophenolate mofetil, azathioprine: For refractory LP requiring long-term systemic immunosuppression as steroid-sparing agents.
Tofacitinib and baricitinib (JAK inhibitors): Emerging evidence for refractory LP, particularly lichen planopilaris (LPP/FFA); multiple case series showing benefit; clinical trials underway.

Research Papers

Key peer-reviewed studies on lichen planus pathogenesis, oral LP malignancy risk, hepatitis C association, and treatment. Each PMID link opens the study on PubMed.

Sugerman PB, et al. The pathogenesis of oral lichen planus. Crit Rev Oral Biol Med. 2002;13(4):350-365. PMID 12191962
van der Waal I. Potentially malignant disorders of the oral and oropharyngeal mucosa; terminology, classification and present concepts of management. Oral Oncol. 2009;45(4-5):317-323. PMID 18674952
Gandolfo S, et al. Risk of oral squamous cell carcinoma in 402 patients with oral lichen planus: a follow-up study in an Italian population. Oral Oncol. 2004;40(1):77-83. PMID 14693244
Lodi G, et al. Systematic review of randomized trials for the treatment of oral lichen planus. J Dent Educ. 2002;66(2):255-260. PMID 11871761
Thyssen JP, Serup J. Lichen planus – clinical overview and drug triggers: a systematic review. Acta Derm Venereol. 2007;87(5):378-395. PMID 17721658
Carrozzo M, Thorpe R. Oral lichen planus: a review. Minerva Stomatol. 2009;58(10):519-537. PMID 19927063
Cribier B, Frances C, Chosidow O. Treatment of lichen planus. An evidence-based medicine analysis of efficacy. Arch Dermatol. 1998;134(12):1521-1530. PMID 9875189
Shengyuan L, et al. Hepatitis C virus and lichen planus: a reciprocal association determined by meta-analysis. Arch Dermatol. 2009;145(9):1040-1047. PMID 19770445
Regezi JA, Sciubba JJ, Jordan RC. Oral Pathology: Clinical Pathologic Correlations. 7th ed. 2017. PubMed: Oral LP histopathology
Salavastru CM, et al. European guidelines for the management of lichen planus: a systematic appraisal. J Eur Acad Dermatol Venereol. 2017;31(10):1596-1607. PMID 28493337
Day T, et al. Lichen planus and the risk of vulvar squamous cell carcinoma: a systematic review. Gynecol Oncol. 2018;148(1):200-208. PMID 29128102
Tziotzios C, et al. Lichen planus and lichenoid dermatoses: clinical overview and molecular basis. J Am Acad Dermatol. 2018;79(5):789-804. PMID 30343749

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