Purple, pruritic papules on the inner wrist.

LICHEN PLANUS

Lichen planus (LP) is a chronic inflammatory condition that can affect the skin, mouth, nails, and genitals, causing itchy, purple, flat-topped papules and plaques, sometimes with lacy white patches in the mouth.

Patients with Hep C have a 4 fold risk of developing lichen planus and vic versa. Patients with LP should be screened for Hep B and C.
The average age at diagnosis of 50–60 years, although it may affect younger adults and children.
It is more common in women than in men (1.4: 1).
Multiple flat-topped red, purple papules symmetric on the inner wrists, ankles, feet and low back are typical.
Pruritus, Koebnerization and post-inflammatory hyperpigmention are common.
It represents a T-cell mediated disorder in which the immune system attacks the skin.
There is a mildly higher incidence of liver disease and dyslipidemia.
Rarely, LP can be medication-induced--lichenoid drug eruption.
Nearly 70% of patients experience resolution within 1 year of presentation.

Clinical

Itchy, violaceous to purple papules and plaques are typical. The surface often has a characteristic white, lacy pattern, called Wickham's stria. As individual lesions heal, residual pigmentation in the form of post inflammatory hyperpigmentation is common. Koebnerization may occur and pruritus may be intense. The inner wrists, ankles, sides of feet, back, oral mucosa, vulva and penis are favored sites. However, the entire body may be covered in severe cases. Thickened, hypertrophic lesions are more common on the legs. A variant of LP in the sun-exposed areas is called lichen planus actinicus. Milia may develop. Rarely bulla may form. The nails may become dystrophic. Very rarely, lesions may occasionally be scaly, putting them in the papulosquamous differential.

Differential/Triggers

An ever-growing number of drugs have been noted to cause lichen planus-like eruptions. These include the new biologics, antimalarials, arsenicals, beta blockers, captopril, furosemide, gold salts, methyl dopa, penicillamine quinidine, sulfonylurea, salsalate and thiazides. One patient's LP was caused by gold-containing cinnamon schnapps. There is some variation in nomenclature. Do these drugs induce lichen planus or do they cause a lichenoid drug eruption? This site has chosen to use the term lichenoid drug eruption.

Liver

Patients with Hep C have a 4 fold risk of developing lichen planus and vic versa.
The proportions of patients with a history of hepatitis B virus or hepatitis C virus infection were 0.4% and 2.4%, respectively in one study.

Post-inflammatory hyperpigmentation is common with LP>

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