# Lichen Planus and Lichenoid Dermatoses

## Overview

Lichen planus (LP) is a chronic, immune-mediated inflammatory dermatosis affecting the skin, mucous membranes, hair follicles, and nails. It is characterized by the classic "5 Ps" — pruritic, polygonal, planar (flat-topped), purple papules and plaques. The histopathologic hallmark is a band-like (lichenoid) lymphocytic infiltrate at the dermoepidermal junction with interface dermatitis. Understanding the broader spectrum of lichenoid dermatoses is essential for differential diagnosis.

## Epidemiology

LP affects approximately 0.5 to 1 percent of the general population, with peak incidence between ages 30 and 60. There is no significant sex predilection, though oral LP is slightly more common in women. The association with hepatitis C virus varies by geography and is strongest in Mediterranean and Asian populations. No clear HLA association has been established in most populations, though HLA-DR1 has been suggested.

## Pathogenesis

LP is driven by a T-cell mediated autoimmune attack against basal keratinocytes. CD8+ cytotoxic T cells target altered or foreign antigens expressed on basal keratinocytes, leading to their apoptosis and the formation of colloid (Civatte) bodies. IFN-gamma and chemokines CXCL9/CXCL10 drive Th1-polarized inflammation, and MHC class II expression is upregulated on keratinocytes. Possible triggers include HCV infection, medications, dental amalgam, and contact allergens, but the autoantigen in idiopathic LP remains unidentified.

## Clinical Features

### Cutaneous Lichen Planus

The classic presentation consists of flat-topped, violaceous, polygonal papules with fine white lines on their surface known as Wickham striae. Preferred sites include the volar wrists, ankles, lower back, and genitalia. The Koebner phenomenon (new lesions at sites of trauma) is common. Variants include hypertrophic LP (thick, verrucous plaques on the shins — extremely pruritic and the most resistant to therapy), atrophic LP, annular LP (ring-shaped lesions, more common on the glans penis), linear LP (following Blaschko lines or from Koebnerization), vesiculobullous LP, actinic LP (photodistributed, more common in Middle Eastern and African populations), LP pigmentosus (diffuse brown-gray hyperpigmentation on the face and intertriginous areas, more common in skin of color), and inverse LP.

### Oral Lichen Planus

The oral mucosa is the most commonly affected mucosal site, involved in 50 to 70 percent of LP patients, and oral LP often persists long after cutaneous disease resolves. The reticular pattern shows white lacy Wickham striae on the buccal mucosa and is often asymptomatic. The erosive pattern, the most clinically significant, presents with painful erythematous erosions. The atrophic or erythematous pattern appears as red, thinned mucosa, often on the gingiva as desquamative gingivitis. Plaque-like and bullous patterns are less common. Erosive oral LP carries approximately a 1 to 2 percent lifetime risk of oral squamous cell carcinoma, warranting long-term surveillance.

### Genital Lichen Planus

Vulvar LP, particularly the erosive vulvovaginal form, causes dyspareunia, scarring, and vaginal synechiae. Penile LP presents as annular lesions on the glans and may cause phimosis. The vulvovaginal-gingival syndrome describes erosive LP affecting the vulva, vagina, and gingiva simultaneously.

### Lichen Planopilaris (LPP)

LPP involves hair follicles and causes cicatricial (scarring) alopecia, presenting with perifollicular erythema, follicular keratosis, and progressive scarring, most commonly on the scalp. Classic LPP presents as multifocal patches of scarring alopecia. Frontal fibrosing alopecia (FFA) causes progressive recession of the frontal and temporal hairline with loss of eyebrows, is increasingly common, and predominantly affects postmenopausal women though it is also seen in men. Graham-Little-Piccardi-Lasseur syndrome combines LPP with non-scarring alopecia of the axillae and pubis plus keratotic follicular papules on the trunk. Trichoscopy shows perifollicular scaling and erythema, loss of follicular ostia, and blue-gray dots.

### Nail Lichen Planus

Nail involvement affects approximately 10 percent of LP patients. Nail matrix involvement causes thinning, ridging, splitting, and pterygium (forward growth of the proximal nail fold onto the nail plate). Twenty-nail dystrophy (trachyonychia), presenting as roughened, sandpapered nails, can be an idiopathic form in children. LP can cause permanent nail loss if left untreated.

## Histopathology

The diagnostic features include interface dermatitis with a band-like lymphocytic infiltrate obscuring the dermoepidermal junction, wedge-shaped hypergranulosis (a thickened granular layer that correlates clinically with Wickham striae), irregular "sawtooth" acanthosis with pointed rete ridges, Civatte bodies (eosinophilic, round, apoptotic keratinocytes at the DEJ), Max Joseph spaces (clefts at the DEJ from basal cell damage), and melanin incontinence with pigment in the dermis from damaged basal cells. Direct immunofluorescence shows fibrinogen deposits in a shaggy pattern along the BMZ — not specific but helpful.

## Lichenoid Drug Eruptions

Lichenoid drug eruptions mimic LP but often show subtle differences: more widespread distribution on the trunk and extremities, less prominent Wickham striae, possible photo-distribution, eczematous features, and less mucosal involvement. Onset is typically weeks to months after starting the offending drug. | Drug Class | Examples |
| --- | --- | --- |
| ACE inhibitors | Enalapril, lisinopril |  |
| Thiazide diuretics | Hydrochlorothiazide |  |
| Antimalarials | Hydroxychloroquine, quinacrine |  |
| Beta-blockers | Atenolol, propranolol |  |
| Gold salts | Aurothioglucose |  |
| NSAIDs | Various |  |
| Checkpoint inhibitors | Anti-PD-1, anti-CTLA-4 (increasingly important) |  |
| TNF-alpha inhibitors | Paradoxical lichenoid reaction |  |
| Sulfasalazine | Sulfasalazine |  |

Common offenders include ACE inhibitors, thiazide diuretics, antimalarials (hydroxychloroquine, quinacrine), beta-blockers, gold salts, NSAIDs, checkpoint inhibitors (anti-PD-1, anti-CTLA-4, increasingly important), TNF-alpha inhibitors (paradoxical lichenoid reaction), and sulfasalazine. Histologically, lichenoid drug eruptions show eosinophils and a deeper perivascular infiltrate, more parakeratosis, and less prominent hypergranulosis compared to classic LP.

## Differential Diagnosis of Lichenoid Dermatoses

The differential includes idiopathic lichen planus, lichenoid drug eruption, lichenoid contact dermatitis (for example from dental amalgam), lichen nitidus (tiny, flesh-colored papules with "ball-in-claw" histology), lichen striatus (a linear lichenoid eruption in children that is self-limited), lichenoid GVHD (chronic graft-versus-host disease), lichenoid keratosis (a benign, solitary involuting lesion), and secondary syphilis, which can show lichenoid histology and should always be considered in the differential.

## Management

### Cutaneous LP

Topical corticosteroids are first-line — high-potency (clobetasol) for the body and medium-potency for thin skin areas. Topical calcineurin inhibitors (tacrolimus or pimecrolimus) are used for genital, facial, or intertriginous LP. Intralesional triamcinolone (5 to 10 mg/mL) is effective for hypertrophic LP. Phototherapy (NB-UVB or PUVA) is used for widespread disease. Systemic therapy for severe or refractory disease includes oral corticosteroids (short course for acute widespread disease), acitretin (especially for hypertrophic LP), methotrexate, mycophenolate mofetil, and hydroxychloroquine.

### Oral LP

High-potency topical corticosteroid gels or pastes (clobetasol, fluocinonide) are applied to erosions. Topical tacrolimus 0.1 percent is used for erosive oral LP, with monitoring for candidal superinfection. Intralesional triamcinolone is used for focal refractory erosions. Systemic therapy for refractory erosive oral LP includes oral prednisone, mycophenolate, or azathioprine. Regular oral surveillance for squamous cell carcinoma is recommended.

### Lichen Planopilaris / FFA

The goal is to halt progression, as scarred areas will not regrow. First-line treatment is hydroxychloroquine 200 to 400 mg/day, with topical and intralesional corticosteroids for active inflammation. Second-line options include doxycycline and mycophenolate. 5-alpha reductase inhibitors (finasteride, dutasteride) have reported benefit in FFA. Pioglitazone, a PPARgamma agonist, is used off-label for LPP and FFA.

<image>Clinical photograph panel of lichen planus variants: (A) classic violaceous, polygonal, flat-topped papules on the volar wrist with Wickham striae visible on close-up, (B) reticular oral lichen planus with white lacy striae on the buccal mucosa, (C) hypertrophic lichen planus showing thick verrucous plaques on the anterior shins, (D) lichen planopilaris with perifollicular erythema and scarring alopecia on the scalp. Show across diverse skin tones.</image>

<image>Histopathology illustration of lichen planus showing the key diagnostic features: band-like lymphocytic infiltrate at the dermoepidermal junction, sawtooth acanthosis with irregular rete ridges, wedge-shaped hypergranulosis, Civatte bodies (apoptotic keratinocytes), and Max Joseph spaces (clefts at DEJ). Label each feature clearly in an H&E-stain style diagram.</image>

<image>Comparison diagram of lichenoid dermatoses showing side-by-side clinical and histologic features of classic lichen planus vs. lichenoid drug eruption vs. lichenoid GVHD. Highlight distinguishing features: eosinophils and deeper infiltrate in drug eruption, satellite cell necrosis in GVHD, and classic sawtooth acanthosis with hypergranulosis in LP.</image>

## Clinical Pearls

Wickham striae (fine white lines on papule surfaces) are pathognomonic for LP; dermoscopy can help visualize them when they are subtle. Always examine the oral mucosa, genitalia, scalp, and nails in any patient diagnosed with cutaneous LP, as involvement may be asymptomatic. Erosive oral LP carries approximately a 1 to 2 percent lifetime risk of squamous cell carcinoma; biannual oral surveillance is recommended. Hepatitis C testing should be performed in all LP patients, as the association is well-established though it varies by geography. In checkpoint inhibitor-induced lichenoid eruptions, the reaction may correlate with antitumor response; collaboration with oncology regarding drug continuation is important. Frontal fibrosing alopecia is increasingly common and may be associated with environmental factors such as sunscreens and fragrances; onset is typically gradual and often diagnosed late.

## References
- Le Cleach L, Chosidow O. Clinical practice: lichen planus. N Engl J Med. 2012;366(8):723-732.
- Kirtschig G. Lichen sclerosus -- presentation, diagnosis and management. Dtsch Arztebl Int. 2016;113(19):337-343.
- Tziotzios C, Lee JYW, Brier T, et al. Lichen planus and lichenoid dermatoses: clinical overview and molecular basis. J Am Acad Dermatol. 2018;79(5):789-804.
- Chiang C, Sah D, Cho BK, Rosenbaum BE, Dusza SW, Scher RK. Hydroxychloroquine and lichen planopilaris: efficacy and introduction of Lichen Planopilaris Activity Index scoring system. J Am Acad Dermatol. 2010;62(3):387-392.