A linear band of erythematous, flat-topped papules on the forearm

An 8-year-old girl presented with an asymptomatic rash on the left forearm with an abrupt onset that had been present for several months and had never been treated. There was no history of trauma to the involved area. She had atopic dermatitis but was otherwise in excellent health. Her immunizations were all up to date and she did not have any adverse reactions to the vaccinations.

On examination, the child was alert and not in distress. There was a linear band of erythematous, flat-topped papules on the left forearm (Figure 1). There were no other cutaneous or systemic abnormalities.

Figure 1.

A linear band of erythematous, flat-topped papules on the left forearm.

DISCUSSION

The abrupt onset of discrete, erythematous, flat-topped papules, 1 to 3 mm in diameter, in a linear distribution is most characteristic of lichen striatus (1). Lichen striatus is a benign, acquired, asymptomatic, T-cell-mediated dermatosis (1). Typically, the lesions begin abruptly with discrete groups of erythematous, smooth or scaly, flat-topped papules which often coalesce to form a continuous or interrupted linear band over a few weeks. The linear band may develop a curved appearance as it characteristically follows the lines of Blaschko (1). Blaschko’s lines are lines of normal cell development in the skin and they represent pathways of epidermal cell migration and proliferation during fetal development. The band is usually a few mm to 2 cm wide and extends from a few cm to the full length of an extremity (1). Sites of predilection include the extremities, followed by, in decreasing order of frequency, trunk, buttocks, face and neck (1). The lesion usually starts on a proximal extremity and extends distally (1). Typically, the eruption is unilateral and solitary (2). In dark-skinned persons, the lesions may be hypopigmented (lichen striatus albus) (Figure 2) (3). Affected patients are often asymptomatic, although some patients experience pruritus. The differential diagnosis includes lichen planus, linear epidermal nevus, inflammatory linear verrucous epidermal nevus, linear psoriasis, atopic dermatitis, allergic dermatitis, linear Darier’s disease and linear porokeratosis.

Figure 2.

Lichen striatus albus presenting as linear streaks of hypopigmented macules on the left arm of a 10-year-old black girl.

Lichen striatus is usually sporadic and idiopathic (4). Predisposing factors include atopy, autoimmunity, genetic predisposition, hypersensitivity reactions, infections, ultraviolet exposure, vaccines, trauma and medications (4). Some authors suggest that a cross reactivity develops between the aforementioned antigens (e.g., vaccines, medications) and shared epitopes on keratinocytes which acts as a triggering factor (4). The condition is most frequently seen in children with a peak age of 5 to 10 years (1). The male to female ratio is approximately 1:2 (2). There is no predominance based on ethnicity or geographic location. Approximately 60% to 85% of patients have a personal or family history of atopy (2).

Lichen striatus is a self-limited condition that often resolves within 1 year (3). When associated with onychodystrophy, the lesion tends to persist longer (5). Postinflammatory hyperpigmentation and hypopigmentation may occur and may last for months to years (3). Relapses are uncommon and may not be in the same location (4).

Treatment is usually not necessary apart from reassurance. For those patients who would like to have therapy for cosmetic reasons, a topical corticosteroid or a topical immunomodulator (tacrolimus or pimecrolimus) is the treatment of choice because it may hasten resolution of the lesion.