Lichen planus

What it is

Lichen planus is a skin disorder of unknown aetiology, most probably being immune mediated.

Causes and risk

Lichenoid drug eruptions have three named causes:

• Gold
• Quinine
• Thiazides

Lichen planus is rarely associated with hepatitis C.

How it presents

The name carries the description: planus is purple, pruritic, papular and polygonal, on flexor surfaces. The lesions are small, polygonal, pruritic, flat-topped, shiny, violet papules that resolve into hyperpigmented macules. The itchy papular rash is most common on the palms, soles, genitalia and flexor surfaces of arms, and the distribution is symmetrical and bilateral.

Other features are:

• Wickham's striae: reticulate white-gray lines, a white-lace pattern on the surface of the rash
• Koebner phenomenon: new skin lesions appearing at the site of trauma
• Nails: thinning of nail plate and longitudinal ridging

The common sites are wrists, ankles, mucous membranes in 60% of patients, that is mouth, vulva and glans, along with nails and scalp. Oral involvement is put at around 50% of patients.