Lichen planus is a chronic inflammatory disease of unknown origin that is characterized by different types of lesions involving the skin and mucosa in middle-aged individuals. The most common lesions are purple papules with well-demarcated, irregular borders, which typically occur on the wrists, lower extremities, and genitoanal region. The surfaces of the lesions often exhibit a pattern of white lines known as Wickham's striae. The disease is diagnosed clinically, but may be confirmed through dermoscopy and punch biopsies. Biopsy also helps detect squamous cell carcinoma, a possible complication of genital lichen planus. Treatment primarily consists of high-dose topical steroids, but may also include oral steroids and phototherapy in cases of extensive or steroid-refractory disease.
- Prevalence: rare disease (occurs in < 1% of the population) 
- Age of onset: 30–60 years 
- Cutaneous lichen planus: ♀=♂
- Oral lichen planus is more common in women
Epidemiological data refers to the US, unless otherwise specified.
Although the exact etiology of lichen planus is unknown, possible etiologic factors include:
Lichen planus may affect the skin, mucosa, scalp, genitalia, and nails, and presents with varying symptoms depending on the subtype of the disease. The condition is chronic and usually manifests with several relapses. 
Cutaneous lichen planus 
May occur simultaneously with other subtypes
- Distribution pattern
Mucosal lichen planus
- Oral lichen planus
- Esophageal lichen planus
Genital lichen planus
The 7 P's of lichen Planus are Pruritic, Polygonal, Planar (flat-topped), Purple Papules, and Plaques.
Subtypes and variants
Lichen planus can manifest with several subtypes, including: 
- Hypertrophic lichen planus (lichen planus verrucosus)
- Mainly affects the scalp of postmenopausal women and presents with pruritus and hair loss
- Frontal fibrosing alopecia (a variant of lichen planopilaris)
Lichen planus is clinically diagnosed based on the presence of typical skin lesions. Additional testing is performed to confirm the diagnosis and rule out other diseases.
- Wedge-shaped hypergranulosis 
- Irregular acanthosis (saw-tooth appearance) 
- Band-like lymphocytic infiltrate at the dermal-epidermal junction 
- Lichen sclerosus
- Drug-induced lichen planus (lichenoid drug eruption): a dermatologic condition that is triggered by certain drugs (e.g., beta blockers, ACE inhibitors, penicillamines) and manifests with lesions that closely resemble lichen planus but are not histologically identical. 
- guttate psoriasis and plaque psoriasis) (
The differential diagnoses listed here are not exhaustive.
- First-line therapy
- Second-line therapy
- Adjunctive therapy: oral antihistamines (e.g., hydroxyzine) to manage pruritus