What You Should Know About Lichen Planus
Lichen planus (LP), one of the so-called “papulosquamous diseases,” is a form of dermatitis which produces a characteristic skin lesion that is classically papular in configuration. This very distinctive eruption is often described with six Ps: pruritic, polygonal, planar, purple, papules and plaques.
Individual lesions of lichen planus classically possess a fine scaly surface that exhibits lacey white striations, aptly called “Wickham’s striae,” or small gray or white pinpoint spots or puncta. Such lesions range from very discrete, individual lesions of 1 to 3 mm in diameter to larger, coalesced lesions of 4 to 5 mm in diameter. Cutaneous lichen planus may involve the wrist and forearms, lumbar area, penis, anterior aspect of the lower legs, ankles, dorsum of the hands and feet, and acral surfaces. Oral lesions occur in approximately one-third of patients with lichen planus and nail involvement occurs in about 10 percent of reported cases.
The majority of nail changes result from damage to the nail matrix, usually involving only one or two fingernails or toenails, but occasionally all nails are affected. Nail changes associated with lichen planus include longitudinal ridging and grooving, splitting, nail thinning and nail loss. In severe cases, the nail may be temporarily or permanently destroyed with prominent pterygium formation.
Lesions on the palms and soles are less common but do occur. In such acral locations, the morphologic expressions of lichen planus are more widely varied than in alternate locations. In many instances, lichen planus of the acral surfaces will have features in common with hypertrophic lichen planus. One will see the formation of large yellow hyperkeratotic papules or plaques rather than the small purple papules clinicians would see with the classic form of lichen planus. Unlike lichen planus arising in alternate locations, pruritus might not be a prominent feature on acral surfaces. In other words, the lesions usually do not itch, are not polygonal and do not have the lacey Wickham’s striae. There may be more familiar-appearing lesions of lichen planus that are adjacent to the lesions on the acral surfaces.
As a general rule, palmoplantar presentations are exceedingly difficult to diagnose. These presentations require close inspection in hopes of finding more typical appearing lesions on non-acral skin. Men and women are equally affected. Men are most often affected by lichen planus between the ages of 20 and 60. In women, the incidence increases with advancing age. While cases of lichen planus have been reported in young children, the condition is generally considered rare in this age group.
The precise cause of lichen planus is essentially unknown, although, many studies have demonstrated that the immunologic system is a central player in the pathogenesis of the condition. Lymphocytes, particularly CD8-positive T-cells, appear to act within involved skin to potentiate the clinical manifestations if not cause them outright.