Lichen planus

Lichen planus (LP) is a dermatosis of unknown etiology, characterized by the presence of purplish papules. In addition to the skin, it can also affect the nails. Mucosal involvement, particularly oral, is rare in the early stages of life. The dermatosis is prevalent in adults and rare in children, with an incidence of 2-11% of all cases of LP. It is caused by the cell-mediated autoimmune response, in which genetic and viral factors play a key role. Triggering factors include viruses, especially hepatitis C (HCV). Case studies report onset after vaccination, especially against hepatitis B. In children, the cause is rarely medication.

Signs and symptoms

The characteristic lesion is a polygonal papule, 1-2 millimetres in size, with a smooth and shiny surface, protruding from the skin and with a typical purplish-red colour. There is sometimes also slight desquamation. The papules may vary in number, and they may be isolated or in distinct clusters or converge in plaques surrounded on the periphery by isolated papules. Typical of LP is the presence on the surface of the lesions of streaks and whitish spots, the so-called Wickham striae, due to thickening of the granular layer. It is more clearly visible on the plaques and using a dermatoscope. Typically affected areas are the flexor aspect of the wrists, legs and back. During the active phases of the disease, the Koebner phenomenon may be observed, i.e. the appearance of papules on trauma-induced excoriations. There is pruritus, usually intense. Lesions in the oral cavity, present in about 40% of children, are often asymptomatic, so they must be investigated. They affect the genian mucosa, usually in the posterior part, and have the appearance of whitish arboriform structures similar to fern leaves or chalk splash. The tongue may also be affected, and whitish, smooth and depapillated patches may be observed. Annular lesions may appear on the lower lip. The nails may be affected in a variable percentage of up to 19% depending on the case, sometimes in an isolated manner. The severity of the clinical profile depends on the affected location (nail matrix, nail bed) and the duration of the lesions. If the matrix is affected, longitudinal streaks and fissures, grooves, and in the more severe forms, diffuse thinning develop. In the more severe forms which lead to destruction of the lamina, a scar may form, dorsal pterygium, due to expansion of the proximal nail fold. The disease presents a variable course with acute forms that may resolve in a few weeks, and chronic forms that persist for months or years with successive flare-ups with new lesions. Resolution occurs with a characteristic sepia brown pigmentation that may remain a long time. Morphological variants such as the verrucous, annular, pigmentary, linear, bullous and follicular forms are reported. Differential diagnosis is with drug-induced lichen, GVHD. In cases of doubt, histological and direct immunofluorescence tests are useful. In the minor forms treatment is based on the use of oral antihistamines and topical steroids, or alternatively tacrolimus. In the acute forms with diffuse lesions, systemic steroids (1 mg/kg/die) are used for 2-6 weeks.

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