++++
Lichen nitidus (Latin nitidus, “shiny” or “glistening”) is an uncommon, usually asymptomatic cutaneous eruption first described by Felix Pinkus in 1901 and further characterized by him in 1907.1,2 Lichen nitidus consists of small, glistening, flesh-colored to pink or reddish-brown papules that may be limited to the penis, genitalia, abdomen, and extremities or, less frequently, may occur as a generalized condition. The histopathologic findings are characteristic. Although the condition is often chronic, the prognosis is good, and no clearly associated systemic illnesses have been documented.
++
Epidemiologic characteristics of lichen nitidus have not yet been defined completely. Lichen nitidus occurs infrequently and has been reported to affect blacks more than Caucasians; children and young adults more than the elderly; and males more than females. The incidence is estimated to be approximately 3.4 cases/10,000 population, based on a 25-year survey of skin diseases in African-Americans.3 The crude ratio of lichen nitidus to lichen planus is 1.7:100, based on pathologic diagnosis of cases evaluated over several decades at the Mayo Clinic.
++
Once considered a tuberculoid reaction, lichen nitidus is currently regarded as a disorder of unknown etiology. The relationship between lichen nitidus and lichen planus has been debated for many years.4 The coexistence of both diseases in some patients, development of lichen planus following generalized lichen nitidus,5 and the clinical similarities to small lichen planus papules were used to support the view that lichen nitidus is a variant of lichen planus. However, most experienced clinicians, as well as research studies, favor the separation of these two diseases as distinct entities based on both clinical and immunodermatopathologic differences and the characteristic and distinctive histologic changes. Table 27-1 summarizes some of these differences and similarities. Another etiologic theory of lichen nitidus proposes that an allergen may cause epidermal and dermal antigen-presenting cells (e.g., Langerhans cells) to activate a cell-mediated response, initiate lymphocyte accumulation, and form discrete inflammatory papules. The presence of large numbers of Langerhans cells in the infiltrate supports this theory.6 Specific cytokines produced by the inflammatory cells influence the immune response and may shift the T lymphocyte response toward the T helper 2 subset that has the potential to produce the superficial dermal granulomas seen in lichen nitidus.7 Functional impairment in cellular immunity has been reported in generalized lichen nitidus,8 and lichenoid photoeruptions similar to lichen nitidus were seen in a patient with HIV infection.9 Rare cases of lichen nitidus associated with atopic dermatitis, Crohn's disease, and juvenile chronic arthritis have been reported. Induction of allergic contact dermatitis by topical application of dinitrochlorobenzene in a patient with lichen nitidus cleared the eruption, presumably by altering the cellular immunity, cellular infiltration, and ...