What is lichen planus?

What is Lichen Planus

Lichen planus is a chronic T-cell mediated inflammatory disorder that affects the skin, mucous membranes (oral, genital, esophageal), scalp, and nails, characterized by immune-mediated destruction of basal keratinocytes. 1, 2

Pathophysiology

• The disease involves a T-cell autoimmune response targeting keratinocytes, with altered self-antigens on basal keratinocyte surfaces (potentially modified by viruses or drugs) serving as the immune targets 3
• Recent research highlights the critical role of IL-17 in the pathogenesis, opening potential therapeutic avenues 4
• Histopathologically, lichen planus shows a characteristic lichenoid interface dermatitis with band-like inflammatory T-cell infiltration in the upper dermis, regardless of clinical presentation 2, 4

Clinical Presentation

Cutaneous lichen planus typically presents in middle-aged adults with characteristic features that differ from lichen sclerosus (which shows porcelain-white papules and plaques with ecchymosis) 5, 6

Oral lichen planus is the most extensively studied phenotype and divides into two main categories 5, 4:

• Hyperkeratotic forms (usually asymptomatic)
• Erosive forms (commonly symptomatic with odynophagia, dysphagia, dysgeusia, and sensitivity to hot/spicy foods)

Esophageal lichen planus represents the most common dermatologic condition affecting the esophagus, occurring in isolation in approximately 33% of cases, with endoscopic findings including narrowed esophageal caliber, pale edematous mucosa that peels upon contact, and thick white exudates 5

Mucosal involvement tends to be persistent and treatment-resistant compared to cutaneous disease, and can lead to scarring in mucosal areas and the scalp (though cutaneous sites typically do not scar) 5, 2

Key Distinguishing Features from Lichen Sclerosus

• Lichen planus does NOT present with the porcelain-white atrophic patches characteristic of lichen sclerosus 5
• Lichen planus does NOT have the same anogenital predilection as lichen sclerosus 7
• Biopsy shows different histopathological features: lichen planus demonstrates band-like lymphocytic infiltration, while lichen sclerosus shows hyperkeratosis, hydropic degeneration of basal cells, sclerosis of subepithelial collagen, and homogenization of collagen in the upper dermis 7

Associated Conditions and Triggers

• Strong association with hepatitis C virus (HCV) infection exists in certain geographical regions, particularly for oral lichen planus 5, 4
• Autoimmune mechanisms are implicated, with T-cell mediated reactions playing a central role 5
• Drugs and contact allergens (such as amalgam) can cause lichenoid reactions that clinically and histologically mimic lichen planus 6, 3
• External triggers including stress have been suggested to precipitate disease 3

Malignant Potential

The World Health Organization categorizes oral lichen planus as an oral potentially malignant disorder, though the risk of malignant transformation is low 4

This contrasts with lichen sclerosus, which carries a well-established 4-5% risk of squamous cell carcinoma 7

Diagnostic Approach

• Biopsy is essential to confirm diagnosis and distinguish from lichenoid drug reactions or lichen sclerosus 7
• Direct immunofluorescence may help distinguish lichen planus from other conditions, particularly in mucosal disease 5
• Clinical and histological features alone cannot always distinguish lichen planus from lichenoid reactions with certainty 3

Disease Burden and Quality of Life

• Certain variants including hypertrophic lichen planus and erosive oral lichen planus follow a more chronic pattern with higher disease burden 6
• The condition significantly affects quality of life, particularly with recalcitrant mucosal or scalp involvement 2
• Esophageal and ophthalmological involvement are likely underdiagnosed 6