Linear Violaceous Papules in a Child

The Diagnosis: Linear Lichen Planus

The patient was clinically diagnosed with linear lichen planus and was started on betamethasone dipropionate ointment 0.05% applied once daily with improvement in both the pruritus and appearance at 4-month follow-up. A biopsy was deferred based on the parents’ wishes.

Lichen planus is an inflammatory disorder involving the skin and oral mucosa. Cutaneous lichen planus classically presents as flat-topped, violaceous, pruritic, polygonal papules with overlying fine white or grey lines known as Wickham striae.¹ Postinflammatory hyperpigmentation is common, especially in patients with darker skin tones. Expected histologic findings include orthokeratosis, apoptotic keratinocytes, and bandlike lymphocytic infiltration at the dermoepidermal junction.¹

An estimated 5% of cases of cutaneous lichen planus occur in children.² A study of 316 children with lichen planus demonstrated that the classic morphology remained the most common presentation, while the linear variant was present in only 6.9% of pediatric cases.³ Linear lichen planus appears to be more common among children than adults. A study of 36 pediatric cases showed a greater representation of lichen planus in Black children (67% affected vs 21% cohort).²

Cutaneous lichen planus often clears spontaneously in approximately 1 year.⁴ Treatment in children primarily is focused on shortening the time to resolution and relieving pruritus, with topical corticosteroids as firstline therapy.^3,4 Oral corticosteroids have a faster clinical response; greater efficacy; and more effectively prevent residual hyperpigmentation, which is especially relevant in individuals with darker skin.³ Nonetheless, oral corticosteroids are considered a second-line treatment due to their unfavorable side-effect profile. Additional treatment options include oral aromatic retinoids (acitretin) and phototherapy.³

Incontinentia pigmenti is characterized by a defect in the inhibitor of nuclear factor–κB kinase regulatory subunit gamma, IKBKG, gene on the X chromosome. Incontinentia pigmenti usually is lethal in males; in females, it leads to ectodermal dysplasia associated with skin findings in a blaschkoid distribution occurring in 4 stages.⁵ The verrucous stage is preceded by the vesicular stage and expected to occur within the first few months of life, making it unlikely in our 5-year-old patient. Inflammatory linear verrucous epidermal nevus usually occurs in children younger than 5 years and is characterized by psoriasiform papules coalescing into a plaque with substantial scale instead of Wickham striae, as seen in our patient.⁶ Lichen striatus consists of smaller, pink to flesh-colored papules that rarely are pruritic.⁷ It is more common among atopic individuals and is associated with postinflammatory hypopigmentation.⁸ Linear psoriasis presents similarly to inflammatory linear verrucous epidermal nevus, with greater erythema and scale compared to the fine lacy Wickham striae that were seen in our patient.⁸