Lichen planus (LP) refers to an idiopathic pruritic, papulosquamous disease with characteristic histopathologic and clinical features, manifesting with a papular skin eruption characteristically found over the flexor surfaces of the extremities, genitalia, and mucous membranes.

• Lichen
• Lichen planus et atrophicus
• LP

LP often manifests with pruritic, flat-topped violaceous papules, but the clinical presentation varies depending on the area involved. Classically, lesions are described with the six "P"s: Purple, pruritic, planar, polygonal, papule, and plaque. In some patients, fine white lines are visible across the surface of the lesions, known as Wickham striae.

• •Usually starts on an extremity and may remain localized or spread to involve other areas over a 1- to 4-mo period
• •Pruritic

Physical findings:

• •Anatomic distribution:
  1. 1.Flexor surface of wrists, forearms, shins, and upper thighs
  2. 2.Neck and back area
  3. 3.Nails (5% to 10% of patients)
  4. 4.Scalp (lichen planopilaris)
  5. 5.Oral mucosa, buccal mucosa, tongue, gingiva, and lips; oral LP can cause extensive desquamative gingivitis
  6. 6.Vulva (Fig. E1), penis (Fig. E2)

Genital mucosa:

• •Lesion configuration:
  1. 1.Linear
  2. 2.Annular (more common)
  3. 3.Reticular pattern noted on oral mucosa and genital area
• •Lesion morphology:
  1. 1.Papules most common presentation (flat, smooth, shiny) (Fig. E3)
  2. 2.Hypertrophic
  3. 3.Follicular
  4. 4.Vesicular
• •Color:
  1. 1.Dark red, bluish red, purplish-violaceous color is noted in cutaneous LP (Fig. E4).
  2. 2.Individual lesions characteristically have white lines visible (Wickham striae) (Fig. E5).
  3. 3.Oral and genital LP has a reticular network of white lines that may be raised or annular in appearance (Fig. E6).
• •Scalp lesions may result in alopecia.
• •The plaques of LP may be hypertrophic but show the characteristic violaceous coloration and intense hyperpigmentation (Fig. E7).

LP is characterized by an immunologic reaction mediated by CD8⁺ T cells. These cells induce keratinocytes to undergo apoptosis. Although the inflammatory reaction is believed to be autoimmune, the antigen targeted by these effector T lymphocytes is unknown.

• •Drug eruption, psoriasis, Bowen disease, leukoplakia, candidiasis, lupus rash, secondary syphilis, seborrheic dermatitis, chronic graft-versus-host disease
• •Table E1 summarizes key features of LP variants

If the diagnosis is questionable, a skin biopsy is performed.

• •Laboratory tests are not specific for the diagnosis of LP
• •Liver function tests
• •Serology for hepatitis B and C
• •Lipid panels screening is useful since increases in serum triglycerides and decreases in HDL (high-density lipoprotein) cholesterol are common in patients with LP

Imaging studies are not helpful in diagnosing LP.

• •Avoid scratching.
• •Use mild soaps and emollients after bathing to prevent dryness.

• •Spontaneous remissions of cutaneous LP occur in >65% of cases within the first year.
• •Spontaneous remission of oral LP usually occurs by 5 yr.
• •∼10% to 20% of patients will have recurrence.

To dermatologist if diagnosis is unclear

• •LP can be remembered as purple, planar, pruritic, polygonal, papules, and plaques (six Ps).
• •Lesions can develop at the site of prior skin injury (Koebner phenomenon).
• •Although there is an increased risk of squamous cell carcinoma in chronic lesions of mucosal LP, transformation to skin cancer is uncommon.

• Lichen Planus (Patient Information)