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Diagnosis: Generalized lichen nitidus

Pathogenesis

Lichen nitidus is an unusual, benign skin eruption of unknown etiology. It's characterized by the slow accumulation of tiny, shiny, flat-topped, skin-colored to hypopigmented, discrete uniform papules that range from 1 to 2 mm in size.^1,2 The eruption may have a fine collarette of scale. Koebnerization (where eruption develops in areas of trauma) is common, often on the hands and forearms.

The eruption occurs most often in children and young adults. Lichen nitidus has a predilection for the penis, lower abdomen, inner thighs, and wrists. However, the eruption may generalize, and individual papules occasionally coalesce to form plaques.^2,3 There are variants where lesions are confined to the palms and soles, where they may coalesce into hyperkeratotic fissured plaques. Nail involvement manifests as beading, longitudinal ridging and nail-fold inflammation. Oral involvement is rare.

Remission is spontaneous and complete after months to years, rarely leaving pigmentary changes. Rare reports have linked lichen nitidus to Crohn's disease and lichen planus. A few case reports demonstrate the clearance of lichen nitidus eruptions with treatment of concomitant tuberculosis or hepatitis C. Familial cases have rarely been reported.

Anecdotes suggest that lichen nitidus is more common in darker pigmented skin. However, this may be related to the more apparent clinical lesions in people of color.

Differential diagnosis^1-5

Lichen planus can be distinguished from lichen nitidus by larger, pruritic, polygonal, purple-grey, flat-topped papules and plaques. Oral involvement in lichen planus is common, and confluent plaques may develop a lacy white reticulated network referred to as Wickham's striae. Lichenoid drug eruptions may overlap clinically with lichen planus or lichen nitidus; however, they are often itchy, and rare in children. Chronic graft-versus-host disease with a lichenoid eruption should be considered in the appropriate clinical setting.

Lichen nitidus may be mistaken for flat warts, 1- to 2-mm skin-colored to slightly hyperpigmented or hypopigmented or pink papules. The warts' spread in a linear fashion by autoinoculation may also be mistaken for the Koebner phenomenon so typical of lichen nitidus. Magnification of flat warts will reveal their rough surface.

Lichen striatus is a benign, self-limited eruption of asymptomatic to slightly pruritic papules that may mimic lichen nitidus. However, it appears in a unilateral distinctive pattern along the lines of Blaschko.

Summer actinic lichenoid eruption may be clinically indistinguishable from lichen nitidus, but there is a predilection for sun-exposed skin sites in dark pigmented individuals from the Middle East and Indian subcontinent during the summer months.⁵ Characteristically, actinic lichenoid eruption improves with sun protection and worsens with sun exposure.

Lichen spinulosis is a discrete, folliculocentric, keratotic papular eruption usually confined to the neck, buttocks, abdomen, hips, knees, and extensor arms. It is a benign disorder that usually remits without treatment at puberty, and is a member of the same family as keratosis pilaris. Lichen spinulosis may occur with atopic dermatitis, and may represent a variant of follicular eczema. Follicular eczema can be widespread, is generally pruritic, and is not as uniform in size or morphology as the papules of lichen nitidus.

Papular sarcoid is rare in children, but it is the most common pattern found in pediatric cutaneous sarcoidosis. The papules often enlarge, though, with a yellow-pink color.