Background
Lichen striatus is a rare, benign, self-limited linear dermatosis of unknown origin that predominantly affects children. [1, 2] It is clinically diagnosed on the basis of its appearance and its characteristic developmental pattern following the lines of Blaschko. [3]
Pathophysiology
The skin is the primary organ system affected by lichen striatus. However, lichen striatus also may involve the nails. [4, 5]
Lesions of lichen striatus follow the lines of Blaschko. [6, 7, 8, 9] Blaschko lines are thought to be embryologic in origin. They are believed to be the result of the segmental growth of clones of cutaneous cells or the mutation-induced mosaicism of cutaneous cells. In lichen striatus, an acquired event (eg, viral infection) may allow an aberrant clone of cutaneous cells to express a new antigen, resulting in the phenotypic skin changes.
Etiology
The etiology of lichen striatus is unknown. Many etiologic or predisposing factors are suggested for lichen striatus. The most commonly accepted hypothesis is the combination of genetic predisposition with environmental stimuli.
Atopy may be a predisposing factor. One group reported that 85% of patients with lichen striatus have a family history of atopic dermatitis, asthma, or allergic rhinitis. However, others have disputed this finding, stating that the incidence of atopy is no greater than that of the general population.
An autoimmune response may also be involved. Lichen striatus has been reported during pregnancy, and it has been postulated that the pregnancy may have triggered an autoimmune response leading to the appearance of the eruption. [10] In addition, lichen striatus has been reported concurrently with vitiligo [11, 12] and after adalimumab [13] and etanercept. [14] It has also been reported 17 months after allogenic peripheral blood stem cell transplant. [15] Some reports have simply suggested that lichen striatus is an inflammatory skin disease mediated by T cells.
An environmental (infectious or traumatic [16] ) etiology has been suggested as well. Familial cases, [17, 18] outbreaks among unrelated children in a shared living environment, and a possible seasonal variation suggest an environmental agent (eg, a virus). The observation of elevated interleukin (IL)-1β levels in lichen striatus biopsy specimens gave some support to the idea of infectious involvement. [7] However, results of viral testing have not conclusively proved this association. In addition, familial episodes of lichen striatus are not always simultaneous, signifying a possible genetic predisposition as a second explanation.
Lichen striatus has been reported to occur shortly after immunization with bacille Calmette-Guérin (BCG) and hepatitis B vaccination, [19] after ultraviolet (UVL) light exposure from a tanning bed, [20] after a prick from a pineapple leaf, after a sting by a bumblebee, [21] and after varicella and influenza infection. [22, 23]
One group of authors suggested that epigenetic mosaicism may be involved, hypothesizing that lichen striatus is triggered by an immunologic reaction to an infection, which triggers methylation or demethylation of a partially silenced genomic element in predisposed patients. [7] A report of concurrent pityriasis rosea and lichen striatus may lend support to this theory. Human herpes viruses 6 and 7 have been implicated in the etiology of pityriasis rosea. The concurrent lichen striatus eruption may have manifested after being triggered by this viral infection. [24]
Epidemiology
Age-, sex-, and race-related demographics
Although lichen striatus is rare in both infants and adults, the disease can occur in persons of any age. [25, 26] Primarily, lichen striatus is a disease of young children. According to some reports, more than 50% of all lichen striatus cases occur between the ages of 5 and 15 years. Other reports have disputed this age range and have claimed that the median age of onset for lichen striatus is 3 years. In a retrospective study (N = 30) of lichen striatus in children (< 18 y), Mendiratta et al found that the 0- to 4-year age group was the one most commonly affected and that the mean age at diagnosis was 5.38 ± 4.22 years. [27]
No consensus exists on sex predilection in lichen striatus. A number of studies have shown a two- to threefold increased incidence in girls as compared with boys, [1, 27] though others have shown an equal sex distribution.
No racial predilection is recognized for lichen striatus.
Prognosis
The prognosis for patients with lichen striatus is excellent. Recovery is complete. The lesions usually regress spontaneously within 1 year (range, 4 wk to 3 y). Relapses may occur, but these are uncommon. Postinflammatory hyperpigmentation and hypopigmentation may last for several months to years after lichen striatus resolves.
Lichen striatus of the nail may take a protracted course, lasting from 6 months to 5 years. [28] Nail involvement resolves spontaneously without deformity.
-
Extensive unilateral lichen striatus that affects both upper and lower extremity. Grouped keratotic lichenoid papules form plaques over leg.
-
Lichen striatus over inner thigh.
-
Hypopigmented lichen striatus over leg.
