What is Lichen planus?

What is Lichen Planus?

Lichen planus is a chronic, T-cell mediated inflammatory autoimmune disease that affects the skin, oral mucosa, genital mucosa, scalp, and nails, characterized by violaceous (dark red/purple), flat-topped, polygonal, pruritic papules and plaques. 1, 2

Clinical Presentation

Cutaneous Features

• Classic lesions are described using the "six P's": planar (flat-topped), purple, polygonal, pruritic, papules, and plaques 2
• Typically affects flexor surfaces of wrists, forearms, and legs with acute onset 2
• Lesions often display Wickham striae - lacy, reticular white lines intersecting across the surface 2
• Cutaneous lichen planus generally does not cause scarring, though mucosal and scalp involvement can lead to permanent scarring 3

Mucosal Involvement

• Oral lichen planus is the most commonly studied phenotype and can present with erosions and white striae in the oral mucosa 1, 3
• Esophageal lichen planus is the most common dermatologic condition affecting the esophagus, occurring in isolation in approximately 33% of cases 3
• Endoscopic findings include narrowed esophageal caliber, pale edematous mucosa with peeling/sloughing upon contact, and thick white exudates 3
• Vulvovaginal involvement can occur with erosions and striae 1

Pathophysiology

Lichen planus is fundamentally a T-cell mediated immunologic disease, though the specific triggering antigen remains unidentified. 4

• Characterized histologically by a rich band-like infiltration of inflammatory T cells in the upper dermis 5
• The American Autoimmunity Association recognizes autoimmune mechanisms as central to pathogenesis 3

Associated Conditions and Triggers

• Hepatitis C virus (HCV) infection shows strong association with oral lichen planus in certain geographical regions 3
• Drug-induced lichenoid reactions can mimic lichen planus and must be differentiated 4
• Immune checkpoint inhibitor (ICI) therapy can trigger lichen planus/lichenoid diseases in up to 6% of treated patients, with mean onset 6-12 weeks after initiation 1

Diagnosis

Clinical Diagnosis

• Classic cutaneous cases may be diagnosed clinically based on characteristic appearance 2
• A 4-mm punch biopsy is required for atypical presentations and to rule out malignancy 6, 2

Histopathologic Features

• Band-like lymphocytic infiltrate in the upper dermis 5
• Hydropic degeneration of basal cells 6
• Direct immunofluorescence (DIF) may help distinguish lichen planus from other conditions, particularly in mucosal disease 3

Important Differential Diagnosis

• Lichen sclerosus must be differentiated - it presents with porcelain-white papules and plaques, often with ecchymosis, and has distinct histopathology including homogenization of collagen in the upper third of dermis 3, 6

Treatment Approach

First-Line Therapy

High-potency topical corticosteroids (clobetasol 0.05% or fluocinonide 0.05%) are the established first-line treatment for all forms of lichen planus. 1, 7, 2, 8

• Gel formulations are preferred for mucosal disease 1, 7
• Solution formulations for scalp disease 1
• Cream/lotion/ointment for other affected areas 1
• Treatment should continue until symptoms improve to Grade 1, then taper over 3 weeks 1, 7

Alternative First-Line Option

• Tacrolimus 0.1% ointment is an effective alternative first-line treatment for all grades, including vulvovaginal and oral lichen planus 1, 7, 2, 8

Second-Line Therapies for Refractory Disease

• Oral antihistamines for symptomatic relief of pruritus 1, 7
• Systemic corticosteroids (prednisone) for severe, widespread disease involving oral, cutaneous, or genital sites 1, 7, 2
• Narrow-band UVB phototherapy if available 1, 7

Third-Line Options for Severe Refractory Cases

Referral to dermatology should be considered for systemic therapy with: 1, 2

• Acitretin (oral retinoid)
• Immunosuppressants: azathioprine, cyclosporine, hydroxychloroquine, methotrexate, mycophenolate mofetil

Clinical Course and Prognosis

• Cutaneous lichen planus may resolve spontaneously within 1-2 years, though recurrences are common 2
• Mucosal lichen planus tends to be more persistent and resistant to treatment 2
• Erosive oral lichen planus and hypertrophic variants may follow a more chronic pattern with higher disease burden 4
• The disease can significantly impact quality of life and carries substantial psychosocial burden 5

Critical Pitfalls to Avoid

• Never initiate treatment without biopsy confirmation - this is mandatory to rule out squamous cell carcinoma, particularly in mucosal disease 6, 7
• Do not confuse lichen planus with lichen sclerosus - they are distinct entities requiring different management approaches 3, 6
• Regular follow-up is essential for mucosal disease due to potential for malignant transformation, though the risk is lower than with lichen sclerosus 3
• Consider drug-induced lichenoid reactions in the differential diagnosis, particularly in patients on new medications or receiving immunotherapy 1, 4