The patient was diagnosed with lichen nitidus, given the characteristic clinical presentation.
Lichen nitidus is a rare chronic inflammatory condition of the skin that most commonly presents in children and young adults and does not seem to be restricted to any sex or race. The classic lesions are described as asymptomatic to slightly pruritic, small (1 mm), skin-colored to hypopigmented flat-topped papules.
Koebner phenomenon is usually seen in which the skin lesions appear in areas of traumatized healthy skin. The extremities, abdomen, chest, and penis are common locations for the lesions to occur. Rarely, the oral mucosa or nails can be involved. It has been described in patients with a diagnosis of Crohn’s disease, Niemann-Pick disease, Down syndrome, and HIV. The rare, generalized purpuric variant has been reported in a few cases associated with interferon and ribavirin treatment for hepatitis C infection and nivolumab treatment for cancer. The pathophysiology of lichen nitidus is unknown.
Lichen nitidus can occur in the presence of other skin conditions like lichen planus, atopic dermatitis, vitiligo, erythema nodosum, and lichen spinulosus. Histopathologic characteristics of lichen nitidus are described as a “ball and claw” of epidermal rete around a lymphohistiocytic infiltrate. Parakeratosis overlying epidermal atrophy and focal basal liquefaction degeneration is also seen.
The differential diagnosis of lichen nitidus includes flat warts, which can present as clusters of small flat-topped papules that can show a pseudo-Koebner phenomenon (where the virus is seeded in traumatized skin). The morphological difference between the condition is that lichen nitidus lesions are usually monomorphic, compared with flat warts, which usually present with different sizes and shapes.
Dr. Catalina Matiz
Patients with a history of allergic contact dermatitis may present with a generalized monomorphic eruption of skin-colored papules (known as ID reaction) that can sometimes be very similar to lichen nitidus. Allergic contact dermatitis tends to respond fairly quickly to topical or systemic corticosteroids, unlike lichen nitidus. There are a few reports that consider lichen nitidus to be a variant of lichen planus, although they have different histopathologic findings. Lichen planus lesions are described as polygonal, pruritic, purple to pink papules most commonly seen on the wrists, lower back, and ankles. Lichen planus can be seen in patients with hepatitis C and may also occur secondary to medication.
Milia are small keratin cysts on the skin that are commonly seen in babies as primary milia and can be seen in older children secondary to trauma (commonly on the eyelids) or medications. Given their size and monomorphic appearance, they can sometimes be confused with lichen nitidus.
Lichen nitidus is often asymptomatic and the lesions resolve within a few months to years. Topical corticosteroids can be helpful to alleviate the symptoms in patients who present with pruritus. In more persistent and generalized cases, phototherapy, systemic corticosteroids, acitretin, isotretinoin, or cyclosporine can be considered.
Dr. Matiz is a pediatric dermatologist at Southern California Permanente Medical Group, San Diego.
References
Chu J and Lam JM. CMAJ. 2014 Dec 9;186(18):E688.
Lestringant G et al. Dermatology 1996;192:171-3.
Peterson JA et al. Proc (Bayl Univ Med Cent). 2021 Aug 25;35(1):70-2.
Schwartz C and Goodman MB. “Lichen nitidus,” in StatPearls. Treasure Island, Fla.: StatPearls Publishing, 2022.