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Patient Story
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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.

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FIGURE 138-1

Lichen planus on the flexor surface of the wrist of a 12-year-old boy. (Used with permission from Weinberg SW, Prose NS, Kristal L, Color Atlas of Pediatric Dermatology, 4th edition, Figure 9-40, New York, NY: McGraw-Hill, 2008.)

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Introduction
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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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Epidemiology
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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

  • 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 20.14

  • There may be a slight female predominance.2,57

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Etiology and Pathophysiology
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  • Usually idiopathic, thought to be a cell-mediated immune response to an unknown antigen.2,5,8

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

  • 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

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

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

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

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

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

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

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

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Diagnosis
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Clinical Features2,8
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  • Classically, the six Ps of LP are planar, purple, ...

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