Epidemiology of Lichen Planus

Epidemiology of Lichen Planus

• The actual incidence and prevalence are not precisely known.
• Existing studies often focus on oral or cutaneous aspects, underrepresenting the full ectodermal range.
• A general estimated prevalence of 1% should be regarded cautiously.
• Prevalence geographically ranges from 0.1% to 4%.
• Most cases (around two thirds) manifest between ages 30 to 60, with peak onset between 55 and 74 years.
• The condition is less prevalent in very young or old age groups.
• There is no observed inclination towards any sex or race, although women tend to experience an earlier onset.

Childhood Lichen Planus

• Accounts for 1% to 5% of all lichen planus cases.
• More frequent in Pacific Indians, comprising around 20% of cases.
• Possibly more common in African American children in the United States.
• Displays no significant sexual predilection.
• Onset typically occurs between 8 and 12 years of age.

Familial Lichen Planus

• Fewer than 100 cases have been reported.
• A strong family history exists in 1.5% of adult cases and 3.8% of pediatric cases.
• Familial forms are characterized by early onset, widespread and often erosive or ulcerative disease, mucosal involvement, and frequent relapses.
• This has led some to classify it as a distinct condition.
• Multiple HLA haplotypes have been identified, including HLA-B27, Aw19, -B18, and -Cw8.
• Nonfamilial cases commonly show HLA-A3, -A5, -A28, -B8, -B16, and Bw35.
• HLA-B8 is more frequent in cases of oral lichen planus alone, while HLA-Bw35 is more frequent in cutaneous lichen planus alone.

Clinical Features of Lichen Planus

• Skin and oral mucosa are most commonly affected.
• It can affect any ectodermal tissue including hair, nails, internal and external genitalia, eyes, and esophagus.
• A detailed history and examination is required to guide therapy, referrals, and monitoring.
• Skin lesions usually develop over several weeks.
• Disease duration depends on lesion location, morphology, and histological pattern.
• Classic cutaneous lesions are well-defined, dull red-violet, flat-topped, polygonal papules.
• Papules often cluster and merge into plaques.
• Wickham striae, which are fine, white, adherent reticulate scales, are seen in developed lesions.
• Wickham striae are highly characteristic and best viewed with dermoscopy.
• Clinical and dermoscopic features correlate with histological findings.
• Wickham striae correspond with orthokeratosis, epidermal thickening, and an increased granular layer.
• The red-violet color results from vascular dilation combined with pigment incontinence.
• Lesions tend to be symmetrically distributed, commonly on the flexural wrists, arms, and legs.
• Other common sites include proximal thighs, trunk, and neck, commonly spares the face and palms.
• Inverse lichen planus affects the axillae, groin, and inframammary region.
• The condition is often extremely pruritic, with the degree of itching related to the extent of involvement.
• A major exception is hypertrophic lichen planus, commonly on the lower extremities, which is intensely pruritic.
• In the acute phase, lichen planus exhibits an isomorphic (Koebner) phenomenon, where trauma induces disease.
• Trauma induces exposure of plasmacytoid DCs to endogenous peptides, such as cathelicidin LL-37, and endogenous antigens, such as DNA and RNA, which stimulate the release of type I IFNs (-α and -β), which propagates disease.
• Usually resolves with postinflammatory hyperpigmentation, more common in darker-skinned individuals.
• Hypopigmentation is rare and warrants considering other diagnoses.

Childhood Lichen Planus in Specific Populations

• Frequent reports originate from the Indian subcontinent.
• This may be due to genetic predisposition, infectious exposures, and social stigma related to pigmentary changes.
• The largest U.S. study found a predominance in African American children, supporting the social implications of pigmentary changes.
• Has similar clinical and histological features to adult lichen planus.
• Skin and oral involvement occur in 42% to 60% and 17% to 30% of cases, respectively.
• Hair and nail involvement are rare, at 2% to 6% and 0% to 19% of cases, respectively.