- Clinical science
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: < 1% 
- Age of onset: 30–60 years 
Epidemiological data refers to the US, unless otherwise specified.
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. 
May occur simultaneously with other subtypes
- Affects the extremities, especially the ankles and flexor wrists, as well as the trunk
- Lesions arranged in linear or circular groups that may coalesce into larger plaques
- Bilateral, symmetrical distribution 
- Lesions often develop in previously traumatized skin ( )
- Oral lichen planus
- Esophageal lichen planus
To remember the most important features of lichen Planus, think of the 7 P's: “Pruritic, Polygonal, Planar (flat-topped), Purple Papules, and Plaques.”
Lichen planus can manifest with several subtypes, including: 
Hypertrophic lichen planus (lichen planus verrucosus)
- Verrucous plaques and nodules that are scaly
- Predominantly affect the shins
- 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.
Lichen sclerosus (et atrophicus) 
- Definition: Lichen sclerosus is a chronic inflammatory disease with characteristic white, atrophic plaques.
- Rare disease
- More common in women (postmenopausal)
- Etiology: unknown (genetic, immunological and hormonal factors likely play a role)
Clinical features 
- Distribution pattern
- Diagnosis 
- Treatment 
- Slightly increased risk of cancer () 
- Destructive scarring
- 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