Lichen nitidus, which literally means “shiny moss,” is a relatively rare, chronic skin eruption that is characterized clinically by asymptomatic, flat-topped, sharply-demarcated, skin-colored papules, which are sometimes described as being “pinpoint.”
Lichen nitidus mainly affects children and young adults. The most common sites of involvement are the trunk, flexor aspects of upper extremities, dorsal aspects of hands, and genitalia, but lesions can occur anywhere on the skin. The lesions also can develop in sites of trauma (Koebner phenomenon), and this can be a significant clinical clue to aid in the diagnosis of lichen nitidus in favor of other conditions which may present as many small papules.1 Nail changes can occur but are rare, presenting as dystrophy, pitting, riding, or loss of nail(s).2
Lichen nitidus can be a challenging diagnosis to make, especially if a practitioner is not used to seeing it. Many dermatologic conditions present with many fine papules, including the other answer choices in the given quiz question (molluscum contagiosum, keratosis pilaris, verruca vulgaris, papular eczema). What allows for a clearer diagnosis of lichen nitidus is the history provided by the patient as well as the exam. Lichen nitidus lesions typically arise without a known trigger and often persist for months while remaining asymptomatic.
Molluscum contagiosum tends to include papules that are larger and more substantial than lichen nitidus papules and may be accompanied by background hyperpigmentation or erythema, known as the “beginning of the end” sign. Keratosis pilaris is commonly thought of as a skin type more so than a skin condition, and is more commonly seen in fair-skinned individuals along the lateral arms and cheeks. It is commonly paired with a background of erythema and skin than tends to be more xerotic. Verruca are typically larger lesions, sometimes with a rough surface, and are not typically shiny. Verruca are more likely to present as a single lesion or a few lesions at a given location, as opposed to lichen nitidus which has many individual papules at a single location. Papular eczema typically is intensely pruritic and is associated with xerosis and atopy.
The cause of lichen nitidus is unknown, and there are no reported genetic factors that contribute to its presentation.3 It is thought to be a subtype of lichen planus, although this is still debated. There is more work that needs to be done to find answers to these questions and to assess what triggers these fine papules to present and in whom.
The dermatoscopic features of lichen nitidus were reported in a series of eight cases and include absent dermatoglyphics, radial ridges, ill-defined hypopigmentation, diffuse erythema, linear vessels within the lesion, and peripheral scaling.4 These features are distinctive in combination and can in some cases be used to clinically diagnose lichen nitidus without the need for a skin biopsy, which is an invasive procedure that should be avoided when possible, especially given the benign nature of lichen nitidus.
If a biopsy is performed, the histologic features that commonly are seen include well-circumscribed granuloma-like lymphohistiocytic infiltrates in the papillary dermis adjacent to ridges, mimicking a “ball-and-claw” formation.1,5
Lichen nitidus generally is self-limiting, with minimal cosmetic disruption; therefore, treatment usually is not necessary. The lesions typically resolve within 1 year of presentation – and often sooner. Topical steroids can be used for symptomatic relief of pruritus, but generally do not hasten resolution of the papules themselves. Additionally, there have been reports in the literature of the successful resolution of lesions using topical calcineurin inhibitors and UVB therapy.
In a case report of an 8-year-old child with histologically confirmed lichen nitidus that had been present for 2 years, pimecrolimus 1% cream was used twice daily for 2 months with improvement and flattening of the papules.6 This report is compelling because the lesions persisted for twice the expected time of resolution without improvement and then showed relatively quick response to pimecrolimus. In a case of a 32-year-old male with lichen nitidus on his penis, tacrolimus 0.1% was used for 4 weeks with resolution of the papules.7 Although given that lichen nitidus can self-resolve in this same time period, it is unclear in this case whether the tacrolimus was the independent cause of the resolution.
With regard to UVB therapy, there have been reports of lichen nitidus resolution after 17-30 irradiation sessions in patients with lesions present for 3-6 months, although again, it is possible that the resolution observed was simply the natural course of the lichen nitidus for these patients rather than a therapeutic benefit of UVB therapy.8,9
Given that lichen nitidus is benign and typically asymptomatic or with mild pruritus, it is reasonable to monitor the lesions without treating them. If the lesions persist beyond 1 year, it also is reasonable to trial therapies, such as topical calcineurin inhibitors and UVB therapy, although using these treatments earlier in the disease course has only limited supporting data and any improvement seen within 1 year of onset may be attributed to the natural disease course as opposed to an effect of the intervention. Considerations of the cost of therapy, as well as the degree to which the patient is bothered by the lesions and how long the lesions have persisted, should be undertaken when considering whether an intervention should be made.