Three-year-old girl develops a rash on her arm

A mother brings in her 3-year-old daughter for a new rash on her right arm. She states that her daughter had smooth skin from birth until 6 weeks ago, when she noticed several bumps in a linear arrangement while bathing her daughter. The child appeared to be asymptomatic. The mother applied hydrocortisone 1% cream daily for 2 weeks with no change. In fact, the bumps became more numerous and prominent during the first 2 to 3 weeks, despite the topical steroid, but now appear to have stabilized. On physical examination, extending from the shoulder to the wrist in a linear arrangement are numerous closely set, 2 mm to 4 mm smooth, flat-topped, pink papules. The remainder of the full skin examination is unremarkable.

What is the most likely etiology?

Can you spot the rash?

Lichen striatus is an uncommon, benign, self-limited, linear dermatosis found most often on the extremities of preschool-aged children. The etiology and pathogenesis are unknown, although a viral-mediated process is thought to be most likely. The eruption follows a linear distribution along the lines of Blaschko.

The lines of Blaschko or Blaschko’s lines, named after Alfred Blaschko, are believed to be the migration pattern of embryologic ectodermal cells and are invisible in normal skin. When somatic mosaicism occurs in ectodermal cells, a patterned dermatosis may occur. Blaschko’s lines follow an S-shaped pattern on the chest, abdomen and flanks, a V-shaped pattern on the back, a wavy pattern on the head, and a curvilinear pattern on the extremities. This is distinct from and unrelated to dermatomes.

Lichen striatus is an uncommon, benign, self-limited, linear dermatosis found most often on the extremities of preschool-aged children.

Photos courtesy of Marissa J. Perman.

Lichen striatus occurs mainly in children aged 4 months to 15 years with the median age of onset from 2 to 4 years of age. Lichen striatus has been found to have a seasonal variation, occurring more commonly in the spring or summer, suggesting a possible viral etiology. However, no clear relationship has been elucidated between the eruption and a specific virus.

One possible explanation for lichen striatus could be due to a somatic mutation during embryogenesis, leading to an aberrant clone of epidermal cells that migrate out along the lines of Blaschko. These cells may then be altered by an infectious agent, vaccination, or other unknown trigger, leading to a cell-mediated immune response and the clinical picture.

On examination, lichen striatus generally appears abruptly over days to weeks as numerous closely set, 1 mm to 4 mm papules, which are smooth, occasionally scaly, flat-topped, skin-colored, pink, or hypopigmented. They appear in a linear distribution involving the extremities and less commonly the trunk, head or neck. Hypopigmented lichen striatus is seen more often in patients with darker skin. The eruption tends to be unilateral but can occasionally be bilateral or consists of several linear parallel bands. The nail unit may also be involved and often portends a longer course. Lichen striatus resolves spontaneously within 12 to 24 months and may lead to residual post-inflammatory hypopigmentation, particularly in patients with darker skin types.

On histopathologic examination, the main features include a dense, band-like lymphocytic and histiocytic infiltrate along the dermal-epidermal junction similar to that seen in lichen planus. The epidermis reveals hyperkeratosis (thickening of the stratum corneum), parakeratosis (retention of nuclei in the stratum corneum) and mild intercellular edema. The lymphocytic infiltrate consists of CD8+ T-cells and often surrounds adnexal structures (hair follicles and eccrine glands) in the deeper dermis, helping to distinguish lichen striatus from lichen planus histopathologically.

The differential diagnosis includes other linear eruptions such as linear lichen planus, linear psoriasis, epidermal nevus, inflammatory linear verrucous epidermal nevus (ILVEN), and blaschkitis. Blaschkitis is usually a recurrent pruritic eruption following the lines of Blaschko on the trunk of adults that consists of several linear bands of scaling papules and vesicles and rarely occurs in children. Some consider lichen striatus and blaschkitis to be similar diseases on a spectrum, or the childhood and adult forms of the same disease.

Treatment involves educating families about the benign course and spontaneous resolution of lichen striatus. In most cases, no therapy is required. If the patient complains of pruritus, a moderate potency topical steroid or topical calcineurin inhibitor — pimecrolimus (Elidel, Novartis) or tacrolimus (Protopic, Astellas) — can be used until symptoms resolve. Physicians should be familiar with lichen striatus to reassure families of the benign nature and limited duration of this condition.

Marissa J. Perman, MD, is a third-year dermatology resident at the University of Cincinnati.

For more information:

• Bolognia JL. Dermatology. 2nd ed. Philadelphia, Pa.: Elsevier; 2008:170-172.
• Müller CS. Br J Dermatol. 2011;164:257-262.
• Keegan BR. Pediatr Dermatol. 2007;24:621-627.

Disclosure: Dr. Perman reports no relevant financial disclosures.

Spot the Rash is a monthly case study featured in Infectious Diseases in Children designed to test your skills in pediatric dermatology issues.