Dermatology MCQ - Inflammatory Dermatoses - Lichen striatus

A 4-year-old child is brought to clinic with a sudden-onset, asymptomatic, linear eruption along the entire length of her right arm. The eruption consists of small, pink, flat-topped, slightly scaly papules. The lesions are not pruritic and the child is otherwise well. What is the most likely diagnosis?

A. Lichen planus
B. Inflammatory linear verrucous epidermal nevus (ILVEN)
C. Lichen striatus
D. Psoriasis
E. Porokeratosis

Correct Answer: C. Lichen striatus

Explanation:

• Lichen striatus is a benign, self-limiting dermatosis of unknown etiology, most commonly seen in children. It classically presents as a sudden onset of small, skin-colored or pink, flat-topped (lichenoid) papules in a continuous or interrupted linear band, following the lines of Blaschko. It is typically unilateral and affects a single extremity. As in the vignette, it is often asymptomatic or only mildly pruritic. The condition resolves spontaneously over months to a few years.

• Why the other options are incorrect:

  • A. Lichen planus: While it presents with violaceous, flat-topped, pruritic papules, it is uncommon in young children and does not follow a strict, continuous Blaschkoid linear pattern on a single extremity. It often involves the wrists, ankles, and oral mucosa.

  • B. Inflammatory linear verrucous epidermal nevus (ILVEN): This condition also follows Blaschko's lines and can appear similar. However, ILVEN is characterized by intensely pruritic, erythematous, and verrucous (warty/rough) papules. It is typically persistent and does not resolve spontaneously, unlike lichen striatus.

  • D. Psoriasis: Psoriasis in a linear configuration (linear psoriasis) is rare. Lesions are typically well-demarcated, erythematous plaques with thick, silvery scale, which is not described here.

  • E. Porokeratosis: Linear porokeratosis follows Blaschko's lines but presents with atrophic patches surrounded by a characteristic, thread-like raised border (the cornoid lamella), which is not a feature in this case.

Key Points for Exams

• Epidemiology: Primarily affects children between 5 months and 15 years of age.

• Pathognomonic Feature: Unilateral, linear, Blaschkoid eruption in a healthy child.

• Prognosis: Excellent. It is a self-limited condition that resolves spontaneously without treatment, usually within 6 to 12 months, but can sometimes last up to 3 years. Post-inflammatory hypopigmentation or hyperpigmentation is common and can persist for months after the active lesions have resolved.

• Management: Reassurance is the cornerstone. Due to its self-resolving nature, active treatment is often not required. For patients with significant pruritus or cosmetic concern, low-potency topical corticosteroids or topical calcineurin inhibitors (e.g., tacrolimus) may be used to reduce inflammation and symptoms.

• Association: It is generally an isolated condition. While some studies suggest a possible link with atopy, it is not associated with systemic disease or internal malignancy.