A 12-year-old boy presents with a rash on his wrists, forearms and ankle for one month (Figure 138-1). The rash itches and he does not know where it comes from. The father states that there are no other members of the family with such a rash now or in the past. The pediatrician recognized the morphology and distribution as that of lichen planus. The papules and plaques on the wrist were pink and purple, planar, pruritic and polygonal. The pediatrician looked inside the mouth and the mucosa was clear with no Wickham’s striae. The boy was started on a mid-potency topical steroid ointment and a follow up appointment was scheduled.

Lichen planus (LP) is a self-limited, recurrent, or chronic autoimmune disease affecting the skin, oral mucosa, and genitalia. LP is generally diagnosed clinically with lesions classically described using the six Ps (planar, purple, polygonal, pruritic, papules, and plaques).

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  LP is an inflammatory dermatosis of skin or mucous membranes that occurs in approximately 1 percent of all new patients seen at health care clinics.¹

  
  
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  Although most cases occur between ages 30 and 60 years, LP can occur at any age with fewer than 4 percent of cases in patients under age 20.^1–4

  
  
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  There may be a slight female predominance.^2,5–7

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  Usually idiopathic, thought to be a cell-mediated immune response to an unknown antigen.^2,5,8

  
  
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  Possible human leukocyte antigen (HLA)-associated genetic predisposition.²

  
  
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  Lichenoid-type reactions may be associated with medications (e.g., angiotensin-converting enzyme inhibitors [ACEIs], thiazide-type diuretics, tetracycline, and chloroquine), metals (e.g., gold and mercury), or infections (e.g., secondary syphilis).^2,8

  
  
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  Associated with liver disease, especially related to hepatitis C virus.^2,8,9

  
  
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  A few cases of LP after hepatitis B vaccination have been reported.¹⁰

  
  
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  LP may be found with other diseases of altered immunity (e.g., ulcerative colitis, alopecia areata, myasthenia gravis).¹

  
  
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  Malignant transformation has been reported in ulcerative oral lesions in men.¹

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  Possible HLA-associated genetic predisposition; however, a positive family history is not consistently found.¹¹

  
  
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  Hepatitis C virus infection, and possibly hepatitis B vaccination, although causal relationship is not established.^6,12

  
  
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  Certain drugs (see the previous section “Etiology and Pathophysiology”).

Clinical Features^2,8

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  Classically, the six Ps of LP are planar, purple, polygonal, pruritic, papules, and plaques (Figure 138-2). These well-demarcated flat-topped violaceous lesions are often covered by lacy, reticular white lines (called Wickham striae or Wickham lines; Figure 138-3).

  
  
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  An initial lesion is usually located on the flexor surface of the limbs, such as the wrists, followed by a generalized eruption with maximal spreading within 2 to 16 weeks.¹

  
  
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  Lesions may demonstrate the Koebner phenomenon (linear distribution) from scratching (Figure 138-4).

  
  
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  Lesions are often hyperpigmented rather than purple or pink in dark-skinned persons, and skin may remain hyperpigmented after lesions resolve (Figure 138-5).

  
  
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  Lesions can also be annular (Figure 138-5).

  
  
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  Skin variants:

  
  
  
  
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    Hypertrophic (Figure 138-6)—Typical papules develop into thicker reddish-brown to purple plaques most commonly on the foot and shins.

    
    
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    Follicular—Pinpoint hyperkeratotic projections often on scalp, may lead to cicatricial alopecia (Figure 138-7).

    
    
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    Vesicular—Vesicles or bullae occur alongside the more typical LP lesions (Figure 138-8).

    
    
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    Actinic—Typical lesions in sun-exposed areas, such as the face, back of hands and arms.

    
    
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    Atrophic—The lesions are atrophic rather than standard plaques.

    
    
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    Ulcerative—Ulcers develop within typical lesions or start as waxy semitranslucent plaques on palms and soles; may require skin grafting.

  
  
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  Mucous membrane variants:

  
  
  
  
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    May be reticular (net-like; Figure 138-9), atrophic, erosive, or bullous. It is almost always bilateral.

    
    
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    Oral lesions may be asymptomatic or have a burning sensation; pain occurs with ulceration.^1,6,9

    
    
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    Found in up to 40 percent of pediatric patients.¹³

    
    
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    Oral LP is often associated with extraoral LP.^4,14,15

  
  
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  Genitalia variants:

  
  
  
  
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    Reticular, annular, papular, or erosive lesions on penis, scrotum, labia, or vagina.

    
    
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    Vulvar/vaginal lesions may be associated with dyspareunia, a burning sensation, and/or pruritus.^1,14

    
    
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    Vulvar and urethral stenosis can also be present.^1,14

  
  
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  Hair and nail variants (Figure 138-10); the latter present in 10 percent of adult patients, but less commonly in pediatric patients:^1,11,13

  
  
  
  
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    Violaceous, scaly, pruritic papules on the scalp can progress to scarring alopecia. Lichen planopilaris (LP of the scalp) can cause widespread hair loss.¹⁶

    
    
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    Nail plate thinning results in longitudinal grooving and ridging; rarely destruction of nailfold and nail bed with splintering (Figure 138-9).

    
    
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    Hyperpigmentation, subungual hyperkeratosis, onycholysis, and longitudinal melanonychia can result from LP.¹